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A Concise Introduction to Logic, Twelfth Edition
Patrick J. Hurley
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ISBN-13: 978-1-285-19654-1
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To: All of the students past and present, who have learned logic from this book.
It is wrong always, everywhere, and for anyone, to believe anything upon insufficient evidence.
–W. K. Clifford
Nothing can be more important than the art of formal reasoning according to true logic.
–Gottfried Wilhelm Leibniz
Brief Contents
Preface xi
Part I INFORMAL LOGIC
1 Basic Concepts 1
1.1 Arguments, Premises, and Conclusions 1 Exercise 1.1 7
3.4 Fallacies of Presumption, Ambiguity, and Illicit Transference 160
Exercise 3.4 174
3.5 Fallacies in Ordinary Language 182
Exercise 3.5 188
Part II
FORMAL LOGIC
4 Categorical Propositions 200
4.1 The Components of Categorical Propositions 200
Exercise 4.1 203
4.2 Quality, Quantity, and Distribution 203
Exercise 4.2 208
4.3 Venn Diagrams and the Modern Square of Opposition 209
Exercise 4.3 219
4.4 Conversion, Obversion, and Contraposition 221
Exercise 4.4 229
4.5 The Traditional Square of Opposition 231
Exercise 4.5 238
4.6 Venn Diagrams and the Traditional Standpoint 243
Exercise 4.6 249
4.7 Translating Ordinary Language Statements into Categorical Form 251
Exercise 4.7 258
5 Categorical Syllogisms 264
5.1 Standard Form, Mood, and Figure 264
Exercise 5.1 269
5.2 Venn Diagrams 272
Exercise 5.2 282
5.3 Rules and Fallacies 285
Exercise 5.3 292
5.4 Reducing the Number of Terms 294
Exercise 5.4 296
5.5 Ordinary Language Arguments 297
Exercise 5.5 300
5.6 Enthymemes 301
Exercise 5.6 303
5.7 Sorites 307
Exercise 5.7 310
6 Propositional Logic 316
6.1 Symbols and Translation 316
Exercise 6.1 326
6.2 Truth Functions 330 Exercise 6.2 339
6.3 Truth Tables for Propositions 342
Exercise 6.3 348
6.4 Truth Tables for Arguments 351
Exercise 6.4 354
6.5 Indirect Truth Tables 358
Exercise 6.5 365
6.6 Argument Forms and Fallacies 367
Exercise 6.6 379
7.1 Rules of Implication I 388
Exercise 7.1 396
7.2 Rules of Implication II 401
Exercise 7.2 406
7.3 Rules of Replacement I 411
Exercise 7.3 417
7.4 Rules of Replacement II 424
Exercise 7.4 429
7.5 Conditional Proof 437
Exercise 7.5 441
7.6 Indirect Proof 443
Exercise 7.6 447
7.7 Proving Logical Truths 449
Exercise 7.7 451
8 Predicate Logic 454
8.1 Symbols and Translation 454
Exercise 8.1 461
8.2 Using the Rules of Inference 464
Exercise 8.2 473
8.3 Quantifier Negation Rule 477
Exercise 8.3 480
8.4 Conditional and Indirect Proof 482
Exercise 8.4 486
8.5 Proving Invalidity 489
Exercise 8.5 494
8.6 Relational Predicates and Overlapping Quantifiers 496
Exercise 8.6 504
8.7 Identity 507
Exercise 8.7 516
Part III INDUCTIVE LOGIC
9 Analogy and Legal and Moral Reasoning 524
9.1 Analogical Reasoning 524
9.2 Legal Reasoning 527
9.3 Moral Reasoning 531 Exercise 9 535
10 Causality and Mill’s Methods 544
10.1 “Cause” and Necessary and Sufficient Conditions 544
10.2 Mill’s Five Methods 546
10.3 Mill’s Methods and Science 556 Exercise 10 561
11 Probability 569
11.1 Theories of Probability 569
11.2 The Probability Calculus 573 Exercise 11 583
12 Statistical Reasoning 587
12.1 Evaluating Statistics 587
12.2 Samples 588
12.3 The Meaning of “Average” 592
12.4 Dispersion 594
12.5 Graphs and Pictograms 599
12.6 Percentages 602 Exercise 12 603
13 Hypothetical/Scientific Reasoning 609
13.1 The Hypothetical Method 609
13.2 Hypothetical Reasoning: Four Examples from Science 612
13.3 The Proof of Hypotheses 618
13.4 The Tentative Acceptance of Hypotheses 621
Exercise 13 624
14 Science and Superstition 632
14.1 Distinguishing Between Science and Superstition 632
14.2 Evidentiary Support 633
14.3 Objectivity 638
14.4 Integrity 643
14.5 Concluding Remarks 647
Exercise 14 649
Answers to Selected Exercises 661
Glossary/Index 705
Preface
The most immediate benefit derived from the study of logic is the skill needed to construct sound arguments of one’s own and to evaluate the arguments of others. In accomplishing this goal, logic instills a sensitivity for the formal component in language, a thorough command of which is indispensable to clear, effective, and meaningful communication. On a broader scale, by focusing attention on the requirement for reasons or evidence to support our views, logic provides a fundamental defense against the prejudiced and uncivilized attitudes that threaten the foundations of our democratic society. Finally, through its attention to inconsistency as a fatal flaw in any theory or point of view, logic proves a useful device in disclosing ill-conceived policies in the political sphere and, ultimately, in distinguishing the rational from the irrational, the sane from the insane. This book is written with the aim of securing these benefits.
About A Concise Introduction to Logic
The new edition of A Concise Introduction to Logic maintains the text’s tradition of careful sequencing, precision, elegance, and clarity, by retaining a number of signature features:
Chapters are organized so that earlier sections provide the foundation for later ones. Later sections can be skipped by instructors opting to do so.
The main points are always presented up front so students cannot possibly miss them.
Relevant and up-to-date examples are used extensively.
Key terms are introduced in boldface type and defined in the Glossary/Index.
Central concepts are illustrated in graphic boxes.
Numerous exercises, many drawn from real-life sources such as newspapers, textbooks, and magazines, are included to perfect student skills—the current edition includes nearly 2,700 exercises.
Biographical vignettes of prominent logicians are included to give logic a human face.
Dialogue exercises illustrate the application of logical principles to real-life situations.
Logic: The key to all learning
Venn diagrams for syllogisms are presented in a novel and more effective way, using color to identify the relevant areas.
Every third exercise is answered in the back of the book so students can check their work.
Important rules and tables are printed on the inside covers for ready access, and, in the current edition, they are also presented on a tear-out card.
New to This Edition
New Digital Solutions for Students and Instructors
Important to this revision is the introduction of several integrated digital products and platforms created to satisfy the diverse needs of today’s students and instructors. The hub of the wheel, so to speak, is MindTap™, a personalized, fully online digital learning platform that offers an interactive eBook, a tutorial program, and homework all in one place. Specifically, MindTap includes the MindTap Reader™ (the interactive eBook), Learning Logic (the tutorial program), Aplia™ (which provides robust homework assignments), and video lectures (devoted to conceptually difficult topics. For more details about this new digital solution, see the Note to the Student, Note to the Instructor, and Versions and Platforms sections later in this preface.
On our new Instructor Companion Site, instructors will find all the tools they need to teach a rich and successful introductory logic course. The protected teaching materials include an Instructor’s Manual , which contains answers to all textbook exercises; Lecture Slides, in Microsoft® PowerPoint®, customizable to fit your particular needs; and a set of image slides that contain all of the photos and art from the text. Also included is the author-created 600-page Test Bank. The multiple-choice tests, which are machine-gradable, can be a great time-saver. The tests in the Test Bank match the Practice Tests available to the students in MindTap in length and format. New to this edition, this Test Bank will be delivered via Cognero™, an online testing system that allows you to author, edit, and manage Test-Bank content. You can create multiple test versions and instantly deliver them through your Learning Management System (LMS) from your classroom, or wherever you may be, with no special installations or downloads required.
New Features
Section-Opening “Previews” induce students to start thinking about the material that follows by connecting the section content to real-life scenarios pertinent to students’ lives. Instructors can use these new previews as discussion starters either in class or online, via MindTap.
The Guide to Important Rules and Argument Forms is presented both as a tear-out card and printed on the inside covers for ready access. That way, if the tear-out card is removed and later misplaced, the rules and argument forms are still available on the inside covers.
New Chapter Content
As you proceed through the book, you will encounter numerous less-visible improvements. Instructors familiar with the text will be most interested in the following revisions:
Further explanation of the Aristotelian/Boolean distinction is provided in a separately published paper entitled “Existential Import: Historical Background.” This paper is available on MindTap and the Instructor Companion Site.
More treatment is given to argument forms/statement forms and their substitution instances.
Three new dialogues replace the older dialogues in Chapter 3. All of the dialogues, including the new ones, were edited by an expert in creative writing.
The treatment of ad populum is expanded to include a presentation of appeal to fear and appeal to tradition.
Expanded treatment is given to the suppressed evidence fallacy.
The idea of vacuous truth is introduced and explained in Chapter 4.
Many new exercises are added to Chapters 4 and 8.
Cues are given in Chapter 6 for producing well-formed formulas.
English examples are given for the first eight rules of inference.
Further instruction, focusing on the main operator of the conclusion, is provided for deriving proofs.
“Change of quantifier rule” is changed to “quantifier negation rule.”
Further treatment is given to the subjectivist (epistemic) theory of probability (Chapter 11).
Hypothetical reasoning in science is more clearly distinguished from hypothetical reasoning in ordinary life (Chapter 13).
The distinction between scientific evidence and religious evidence is approached differently; cures in traditional Eastern medicine are mentioned in connection with placebos (Chapter 14).
The problem of scientists faking evidence is explored (Chapter 14).
A complete list of improvements is given in the Instructor’s Manual.
Note to the Student
Imagine that you are interviewing for a job. The person across the desk asks about your strengths, and you reply that you are energetic, enthusiastic, and willing to work long hours. Also, you are creative and innovative, and you have good leadership skills. Then the interviewer asks about your weaknesses. You hadn’t anticipated this question, but after a moment’s thought you reply that your reasoning skills have never been very good.
The interviewer quickly responds that this weakness could create big problems.
“Why is that?” you ask.
“Because reasoning skills are essential to good judgment. And without good judgment your creativity will lead to projects that make no sense. Your leadership skills will direct our other employees in circles. Your enthusiasm will undermine everything we have accomplished up until now. And your working long hours will make things even worse.”
“But don’t you think there is some position in your company that is right for me?” you ask.
The interviewer thinks for a moment and then replies, “We have a competitor on the other side of town. I hear they are hiring right now. Why don’t you apply with them?”
The point of this brief dialogue is that good reasoning skills are essential to doing anything right. The business person uses reasoning skills in writing a report or preparing a presentation; the scientist uses them in designing an experiment or clinical trial, the department manager uses them in maximizing worker efficiency, the lawyer uses them in composing an argument to a judge or jury. And that’s where logic comes in. The chief purpose of logic is to develop good reasoning skills. In fact, logic is so important that when the liberal arts program of studies was formulated fifteen hundred years ago, logic was selected as one of the original seven liberal arts. Logic remains to this day a central component of a college or university education.
From a more pragmatic angle, logic is important to earning a good score on any of the several tests required for admission to graduate professional schools—the LSAT, GMAT, MCAT, GRE, and so on. Obviously, the designers of these tests recognize that the ability to reason logically is a prerequisite to success in these fields. Also, logic is a useful tool in relieving what has come to be called math anxiety. For whatever reason, countless students today are terrified of any form of reasoning that involves abstract symbols. If you happen to be one of these students, you should find it relatively easy to master the use of logical symbols, and your newly found comfort with these symbols will carry over into the other, more difficult fields.
Before commencing your study of logic, be sure to check out MindTap (www.cengage .com/mindtap). This highly robust Internet platform supports all of the supplements that accompany your textbook. It has the advantage of being able to play on any Internetenabled device including desktops, laptops, and mobile devices, which allows you to learn anywhere, at any time, and on your terms. Some of the products offered on
MindTap are Learning Logic, a set of video lectures that presents challenging subjects in logic, an eBook (MindTap Reader) containing everything in the textbook, and practice tests for every chapter. Also available is a supplement called Logic and GraduateLevel Admission Tests, which shows how the principles you will learn in studying logic can be used to answer questions on the LSAT, GMAT, MCAT, and GRE.
Among the MindTap offerings that I would especially urge you to investigate is Learning Logic. This is an interactive tutorial program that virtually teaches the entire course in a very user-friendly way. It tracks the textbook chapter by chapter, but your computer must be equipped with speakers or headphones, because the audio component is essential.
Because proficiency in logic involves developing a skill, it helps to work through the practice problems in Learning Logic and the exercises in the textbook more than once. This will help you see that good reasoning (and bad reasoning, too) follows certain patterns whose identification is crucial to success in logic. As you progress, I think you will find that learning logic can be lots of fun, and working with the online resources of MindTap should enhance your overall learning experience.
Note to the Instructor
The image on the front cover is intended to convey the message that logic is the key to all learning. Hopefully, by the end of their course, your students will be persuaded that this claim is true. To promote the achievement of this goal, the new edition features “previews,” at the beginning of chapter sections, that are designed to engage the students’ interest, promote prior learning, and induce them to read the section that follows. The instructor can also use these previews as springboards for in-class lectures. While the inclusion of these previews is probably the most visible change in the new edition, as you proceed through the book you will encounter numerous less visible improvements. Many of them are listed above in “New Chapter Content,” and a complete list is given in the Instructor’s Manual.
As I mentioned above, a central feature of this revision is the introduction of MindTap, a personalized, fully online digital learning platform that offers an interactive eBook, a tutorial program, and homework all in one place. See the “Digital Packaging Options” section below for help in deciding which ISBN to select for your course based on the digital assets you want your students to access.
One of the more noteworthy offerings on MindTap is Learning Logic. This tutorial program virtually teaches the course, and it is especially helpful for students who have difficulty mastering logical principles directly from the textbook or from classroom lectures alone. The program is multimedia, which means that students learn not only by seeing but also by hearing. In addition, it incorporates easy-to-use forward and reverse buttons, so students who have failed to understand something the first time can easily go back to hear the lesson repeated. Learning Logic contains over two thousand practice problems not contained in the textbook, and students get immediate feedback for correct and incorrect answers.
Another great product available on MindTap is Aplia, an online homework program that improves student comprehension by increasing effort and engagement. Students get immediate feedback on their work—not only what they got right or wrong—but why; and they can choose to see another set of related problems if they want further practice. Aplia’s simple-to-use course management interface allows instructors to post announcements, host student discussions, e-mail students, and manage the grade book. Personalized help is available from a knowledgeable and friendly support team. To learn more, ask your Cengage Learning sales representative for a demonstration, or view a specific demonstration for this book at www.aplia.com.
Also note that the Instructor’s Companion Website contains the Instructor’s Manual and the Test Bank. The Instructor’s Manual includes answers to all the book’s exercises and a complete list of the improvements introduced in this edition. The author-generated Test Bank includes numerous tests for each chapter in the book.
Let me now turn to alternate ways of approaching the textbook. In general, the material in each chapter is arranged so that certain later sections can be skipped without affecting subsequent chapters. For example, those wishing a brief treatment of natural deduction in both propositional and predicate logic may want to skip the last three sections of Chapter 7 and the last four (or even five) sections of Chapter 8. Chapter 2 can be skipped altogether, although some may want to cover the first section of that chapter as an introduction to Chapter 3. Finally, Chapters 9 through 14 depend only slightly on earlier chapters, so these can be treated in any order one chooses. However, Chapter 14 does depend in part on Chapter 13.
Type of Course
traditional logic course
recommended material
Chapter 1
Chapter 3
Chapter 4
Chapter 5
Chapter 6
Secions 7.1–7.4
Informal logic course, criticalreasoning course
Chapter 1
Chapter 2
Chapter 3
Chapter 4
Sections 5.1–5.3
Sections 5.5–5.6
Sections 6.1–6.4
Section 6.6
Chapter 9
Chapter 12
Chapter 13
Chapter 14
Critical Thinking and Writing Supplement
Course emphasizing modern formal logic
Chapter 1
Sections 4.1–4.3
Section 4.7
Sections 6.1–6.5
Chapter 7
Chapter 8
Truth Trees Supplement
Optional material
Chapter 2
Sections 7.5–7.7
Chapters 9–14
Section 5.4
Section 5.7
Section 6.5
Chapter 10
Chapter 11
Chapter 3
Sections 4.4–4.6
Sections 5.1–5.2
Section 5.7
Section 6.6
Digital Options
A Concise Introduction to Logic is available in multiple formats, including as a printed textbook that can be bought alone [ISBN: 9781285196541], and it can be combined with digital solutions in a variety of ways, including the following:
1. textbook + Mindtap [ISBN: 9781305121768]. Includes, in addition to the printed textbook, access to the MindTap course, with Learning Logic (the tutorial), Aplia quizzing assignments, Videos (covering difficult-to-master topics in logic), chapter learning path activities, quizzing, Truth Trees, Critical Thinking and Writing, and the full-text interactive eBook (MindTap Reader).
2. textbook + aplia [ISBN: 9781285992273]. Includes, in addition to the printed textbook, access to the Aplia course (with automatically graded assignments featuring detailed, immediate feedback on every question), the course management interface (which allows instructors to post announcements, upload course materials, host student discussions, e-mail students, and manage the grade book), and the full-text interactive eBook (MindTap Reader).
3. Mindtap (alone) [ISBN: 9781285427355]. Available with the interactive eBook (MindTap Reader), this option includes everything in Option 1 except the printed textbook. Available only at www.cengagebrain.com, this option can be a cost-saving choice for students.
4. a plia (alone) [ISBN: 9781285427577]. Available with the interactive eBook (MindTap Reader), this option includes everything in Option 2 except the printed textbook. Available only at www.cengagebrain.com, this option can be a cost-saving choice for students.
5. Instructor Companion Site [ISBN: 9781305072855]. This password-protect website for instructors features all of the Instructor’s Manual, Lecture Slides, and Test Bank delivered via Cognero. Access all of your instructor resources by logging into your account at www.cengage.com/login.
6. Custom Options. Cengage Learning offers custom solutions for your course—whether it’s making a small modification to A Concise Introduction to Logic to match your syllabus or combining multiple sources to create something truly unique. You can also pair your custom text with our digital solutions such as MindTap and Aplia. For more information, visit www.cengage.com/custom.
7. CengageBrain. Let this be your students’ online source for an à la carte offering of all of the products they need for a successful logic course. Visit www.cengagebrain.com.
Contact your personal Learning Consultant, sites.cengage.com/RepFinder/, for more information about all available options, pricing, and assistance in selecting the best solutions for your students and your course.
Acknowledgments
For their reviews and suggestions leading to this twelfth edition I want to thank the following:
Ida Baltikauskas, Century College; Peter Barry, Saginaw Valley State University; Jeff Broome, Arapahoe Community College; Loren Cannon, Humboldt State University; Darryl Cohen, Mesa Community College; Michael Coledu, Reedley College; Louis Colombo, Bethune-Cookman University; Jack Crumley, University of San Diego; Drew Dalton, Florida Southern College; Ray Darr, Southern Illinois University; Jeffrey Easlick, Saginaw Valley State University; William Ferraiolo, San Joaquin Delta College; Albert Filice, Mesa Community College; Paul Gass, Coppin State University; Dimitria Gatzia, The University of Akron Wayne College; Alexander Hall, Clayton State University; Ryan Hickerson, Western Oregon University; Jeremy Hovda, Minneapolis Community & Technical College; Debby Hutchins,
Gonzaga University; Ron Jackson, Clayton State University; William Jamison, University of Alaska Anchorage; Richard A. Jones, Howard University; Patrick Kenny, Onondaga Community College; Kristin Klamm-Doneen, Anoka Ramsey Community College; Stephen Leach, UTPA; Chris Lorkowski, Kent State University–Trumbull Campus; Ian MacKinnon, The University of Akron; Leemon McHenry, California State University Northridge; Daniel Metz, Metropolitan State College of Denver; Alexander Miller, Piedmont Technical College; Nathaniel Nicol, Washington State University; Tim O’Neill, Rochester Community and Technical College; Stephen Pacheco, University of San Diego; Joseph Pak, Los Angeles City College; Christopher Pallotti, Los Angeles Valley College/CSUN; Christopher Pearson, Southern Illinois University Edwardsville; Fernando Rincon-Tellez, Piedmont Technical College; Matthew Roberts, Patrick Henry College; Michael Rooney, Pasadena City College; Candice Shelby, University of Colorado Denver; Robert Skipper, St. Mary’s University; Matthew Slater, Bucknell University; Kent Slinker, Pima Community College; Paul Studtmann, Davidson College; Weimin Sun, California State University, Northridge; Corine Sutherland, Cerritos College; Robert Sutton, Cape Fear Community College; Mojgan Taheri, California State University, Northridge; J. Ramon Tello, Shasta College; Mark Thames, El Centro College; Michael Thune, Joliet Junior College; William Vanderburgh, Wichita State University; Michael Ventimiglia, Sacred Heart University; Susan Vineberg, Wayne State University; Mark Vopat, Youngstown State University; Dennis Weiss, York College of Pennsylvania; Derrick Willis, Temple College; Sandra Woien, Mesa Community College; Julie Yoo, California State University, Northridge; Xiaoyu Zhu, Antelope Valley College.
Of course any errors or omissions that may remain are the result of my own oversight. Those who have contributed reviews and suggestions leading to the eleven previous editions, and to whom I express my continued thanks, are the following:
James T. Anderson, University of San Diego; Carol Anthony,Villanova University; Joseph Asike, Howard University; Harriet E. Baber, University of San Diego; Kent Baldner, Western Michigan University; James Baley, Mary Washington College; Jerome Balmuth, Colgate University; Victor Balowitz, State University of New York, College at Buffalo; Ida Baltikauskas, Century College; Gary Baran, Los Angeles City College; Robert Barnard, University of Mississippi; Gregory Bassham, Kings College; Thora Bayer, Xavier University of Louisiana; David Behan, Agnes Scott College; John Bender, Ohio University, Athens; James O. Bennett, University of Tennessee, Knoxville; Victoria Berdon, IUPU Columbus; Robert Berman, Xavier University of Louisana; Kevin Berry, Ohio University; Joseph Bessie, Normandale Community College; John R. Bosworth, Oklahoma State University; Andrew Botterell, University of Toronto; Tom Browder, University of Nevada, Las Vegas; Harold Brown, Northern Illinois University; Kevin Browne, Indiana University Southeast; Ken Buckman, University of Texas, Pan American; Robert Burch, Texas A&M University; Keith Burgess-Jackson, University of Texas, Arlington; Michael Byron, Kent State University; Scott Calef, Ohio Wesleyan University; Gabriel Camacho, El Paso Community College; James Campbell, University of Toledo; Loren Cannon, Humboldt State University; Charles Carr, Arkansas State University; William Carroll, Coppin State University; Jennifer Caseldine-Bracht, IUPU Fort Wayne; John Casey, Northern Illinois University; Robert Greg Cavin, Cypress College; Ping-Tung Chang, University of Alaska; Prakash Chenjeri, Southern Oregon University; Drew Christie, University of New Hampshire; Timothy Christion, University of North Texas; Ralph W. Clarke, West Virginia University; David Clowney, Rowan University; Michael Cole, College of William and Mary; Michael J. Colson, Merced College; William F. Cooper, Baylor University; William Cornwell, Salem State College; Victor Cosculluela, Polk Community College; Mike Coste, Front Range Community College; Ronald R. Cox, San Antonio College; Houston A. Craighead, Winthrop University; Donald Cress, Northern Illinois University, DeKalb; Jack Crumley, University of San Diego; Linda Damico, Kennesaw State
University; William J. DeAngelis, Northeastern University; Joseph DeMarco, Cleveland State University; Paul DeVries, Wheaton College; Jill Dieterle, Eastern Michigan University; Mary Domski, University of New Mexico; Beverly R. Doss and Richard W. Doss, Orange Coast College; Paul Draper, Purdue University; William A. Drumin, King’s College, Pennsylvania; Clinton Dunagan, Saint Philips College; Paul Eckstein, Bergen Community College; Anne M. Edwards, Austin Peay State University; Michael Epperson, California State University, Sacramento; Lenore Erickson, Cuesta College; Cassandra Evans, San Diego City College; Frank Fair, Sam Houston State University; Evan Fales, University of Iowa; Thompson Faller, University of Portland; Lewis S. Ford, Old Dominion University; Gary Foulk, Indiana State University, Terre Haute; Timothy C. Fout, University of Louisville; LeAnn Fowler, Slippery Rock University; Craig Fox, California University of Pennsylvania; Thomas H. Franks, Eastern Michigan University; Bernard D. Freydberg, Slippery Rock University; Thomas J. Frost, Biola University/Long Beach City College; Dick Gaffney, Siena College; George Gale, University of Missouri–Kansas City; Pieranna Garavaso, University of Minnesota at Morris; Paul Gass, Coppin State University; Joseph Georges, El Camino College; Kevin Gibson, University of Colorado; James Granitto, Santiago Canyon College; Victor Grassian, Los Angeles Harbor College; Catherine Green, Rockhurst University; James Greene, Northern Michigan University; Harold Greenstein, SUNY Brockport; J. Randall Groves, Ferris State University; Shahrokh Haghighi, California State University; Alexander W. Hall, Clayton State University; Dean Hamden, Montclair State University; Courtney Hammond, Cuyamaca College; Ken Hanly, Brandon University; Anthony Hanson, West Valley College; Merle Harton, Edward Waters College; Larry Hauser, Alma College; Deborah Heikes, University of Alabama in Huntsville; Ronald Hill, University of San Diego; Lawrence Hinman, University of San Diego; Lynn Holt, Mississippi State University; John B. Howell, III, Southwestern Baptist Theological Seminary; R. I. G. Hughes, University of South Carolina, Columbia; Peter Hutcheson, Texas State University; Debby D. Hutchins, Boston College; William H. Hyde, Golden West College; Ron Jackson, Clayton State University; William Jamison, University of Alaska Anchorage; Sandra Johanson, Green River Community College; Gary Jones, University of San Diego; Richard Jones, Howard University; Russel Jones, University of Oklahoma; Glenn C. Joy, Texas State University, San Marcos; Olin Joynton, North Harris County College; Grant Julin, St. Francis University; Joseph Keim Campbell, Washington State University; Glen Kessler, University of Virginia; Charles F. Kielkopf, Ohio State University; Moya Kinchla, Bakersfield College; Bernard W. Kobes, Arizona State University; Keith W. Krasemann, College of DuPage; Richard La Croix, State University College at Buffalo; Sandra LaFave, West Valley College, Saratoga, California; William Lawhead, University of Mississippi; Stephen Leach, UTPA; Richard Lee, University of Arkansas; Lory Lemke, University of Minnesota, Morris; Robert Levis, Pasadena City College; Chenyang Li, Monmouth College, Monmouth, Illinois; Chris M. Lorkowski, Kent State University; Keane Lundt, Massachusetts College of Liberal Arts; Ardon Lyon, City University of London; Scott MacDonald, University of Iowa; Ian MacKinnon, The University of Akron; Krishna Mallick, Salem State College; Thomas Manig, University of Missouri–Columbia; James Manns, University of Kentucky; Dalman Mayer, Bellevue Community College; Larry D. Mayhew, Western Kentucky University; Leemon McHenry, California State University, Northridge; Robert McKay, Norwich University; Rick McKita, Colorado State University; Phillip McReynolds, Pennsylvania State University; Erik Meade, Southern Illinois University–Edwardsville; Noel Merino, Humboldt State University; Kenneth R. Merrill, University of Oklahoma; Thomas Michaud, Wheeling Jesuit College; Dolores Miller, University of Missouri–Kansas City; George D. Miller, DePaul University; Richard Miller, East Carolina University; Frederick Mills, Bowie State University; Jeff Mitchell, Arkansas Tech University; John Mize, Long Beach City College; Allyson Mount, Keene State College; Seyed Mousavian, University of Alberta; Dwayne Mulder, California State University, Fresno; John D. Mullen, Dowling College; Madeline Muntersbjorn, University of Toledo; Henry Nardone, Kings College;
Theresa Norman, South Texas Community College; David O’Connor, Seton Hall University; Len Olsen, Georgia Southern University; Elane O’Rourke, Moorpark College; Brendan O’Sullivan, Rhodes College; Stephen Pacheco, University of San Diego; Rodney Peffer, University of San Diego; Linda Peterson, University of San Diego; Robert G. Pielke, El Camino College; Cassandra Pinnick, Western Kentucky University; Nelson Pole, Cleveland State University; Norman Prigge, Bakersfield State University; Gray Prince, West Los Angeles College; R. Puligandla, University of Toledo; T. R. Quigley, Oakland University; Nani Rankin, Indiana University at Kokomo; Robert Redmon, Virginia Commonwealth University; Bruce Reichenbach, Augsburg College; Herminia Reyes, San Diego State University; David Ring, Southern Methodist University; Tony Roark, Boise State University; Michael Rooney, Pasadena City College; Phyllis Rooney, Oakland University; Beth Rosdatter, University of Kentucky; Michelle M. Rotert, Rock Valley College; Paul A. Roth, University of Missouri–Saint Louis; Daniel Rothbart, George Mason University; Robert Rupert, University of Colorado, Boulder; Sam Russo, El Camino College; Frank Ryan, Kent State University; Eric Saidel, George Washington University; Kelly Salsbery, Stephen F. Austin State University; Paul Santelli, Siena College; Stephen Satris, Clemson University; Phil Schneider, Coastal Carolina University; Philip Schneider, George Mason University; James D. Schumaker, University of North Carolina at Charlotte; Stephanie Semler, Radford University; Pat Sewell, University of North Texas; Elizabeth Shadish, El Camino College; Joseph G. Shay, Boston College; Janet Simpson, Suffolk County Community College; Aeon Skoble, Bridgewater State College; Dennis L. Slivinski, California State University, Channel Islands; Arnold Smith, Youngstown State University; John-Christian Smith, Youngstown State University; Joshua Smith, Central Michigan University; Paula Smithka, University of Southern Mississippi; Eric W. Snider, University of Toledo; Bob Snyder, Humboldt University; Joseph Snyder, Anne Arundel Community College; Lynne Spellman, University of Arkansas; David Stern, University of Iowa; James Stuart, Bowling Green State University; Paul Studtmann, Davidson College; Krys Sulewski, Edmonds Community College; John Sullins, Sonoma State University; John Sweigart, James Madison University; Clarendon Swift, Moorpark College; Wayne Swindall, California Baptist College; Brian Tapia, Foothill College; Bangs Tapscott, University of Utah; J. Ramon Tello, Shasta College; Jan Thomas, University of Arkansas at Little Rock; Phil Thompson, Eastern Illinois University; Richard Tieszen, San Jose State University; Larry Udell, West Chester University; Ted Ulrich, Purdue University; Robert Urekew, University of Louisville; William Uzgalis, Oregon State University; William Vanderburgh, Wichita State University; Mark Vopat, Youngstown State University; Thomas H. Warren, Solano College; Andrew J. Waskey, Dalton State University; Roy Weatherford, University of South Florida; Chris Weigand, Our Lady of the Lake University; David Weinburger, Stockton State College; Paul Weirich, University of Missouri–Columbia; David Weise, Gonzaga University; Robert Wengert, University of Illinois at Urbana–Champaign; Shannon Grace Werre, Edmonds Community College; Gerald Joseph Williams, Seton Hall University; Frank Wilson, Bucknell University; W. Kent Wilson, University of Illinois, Chicago; Katherine D. Witzig, Southwestern Illinois College; Stephen Wykstra, Calvin College; Marie Zaccaria, Georgia Perimeter College; Jeffrey Zents, University of Texas.
Finally, it has been a pleasure working with publisher Clark Baxter, former philosophy editor Joann Kozyrev, new philosophy editor Debra Matteson, content developer Florence Kilgo, content project manager Jill Quinn, production supervisor Greg Hubit, copy editor Marne Evans, proofreader Debra Nichols, content coordinator Joshua Duncan, dialogue specialist Karen Mockler, and exercise checker Steven Livaditis. Most of all, I want to thank my wife, Linda Peterson, for her countless suggestions and support.
Basic Concepts
1.1 Arguments, Premises, and Conclusions
1.2 Recognizing Arguments
1.3 Deduction and Induction
1.4 Validity, Truth, Soundness, Strength, Cogency
1.5 Argument Forms: Proving Invalidity
1.6 Extended Arguments
1.1 Arguments, Premises, and Conclusions
PREVIEW Suppose a student with whom you are in a long-term relationship happens to see you sitting close to someone else in the library. The person you have been dating for months now accuses you of cheating and threatens to break off the relationship. You, in turn, try to prove that the event in the library was perfectly innocent and amounted to nothing. To do this, you need an argument. In this section you will learn about arguments and their basic components, premises and conclusions.
Logic may be defined as the organized body of knowledge, or science, that evaluates arguments. All of us encounter arguments in our day-to-day experience. We read them in books and newspapers, hear them on television, and formulate them when communicating with friends and associates. The aim of logic is to develop a system of methods and principles that we may use as criteria for evaluating the arguments of others and as guides in constructing arguments of our own. Among the benefits to be expected from the study of logic is an increase in confidence that we are making sense when we criticize the arguments of others and when we advance arguments of our own.
An argument, in its simplest form, is a group of statements, one or more of which (the premises) are claimed to provide support for, or reasons to believe, one of the others (the conclusion). Every argument may be placed in either of two basic groups: those in which the premises really do support the conclusion and those in which they do not, even though they are claimed to. The former are said to be good arguments (at least to that extent), the latter bad arguments. The purpose of logic, as the science that
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evaluates arguments, is thus to develop methods and techniques that allow us to distinguish good arguments from bad.
As is apparent from the given definition, the term argument has a very specific meaning in logic. It does not mean, for example, a mere verbal fight, as one might have with one’s parent, spouse, or friend. Let us examine the features of this definition in greater detail. First of all, an argument is a group of statements. A statement is a sentence that is either true or false—in other words, typically a declarative sentence or a sentence component that could stand as a declarative sentence. The following sentences are statements:
Chocolate truffles are loaded with calories.
Melatonin helps relieve jet lag.
Political candidates always tell the complete truth.
No wives ever cheat on their husbands.
Tiger Woods plays golf and Maria Sharapova plays tennis.
The first two statements are true, the second two false. The last one expresses two statements, both of which are true. Truth and falsity are called the two possible truth values of a statement. Thus, the truth value of the first two statements is true, the truth value of the second two is false, and the truth value of the last statement, as well as that of its components, is true.
Unlike statements, many sentences cannot be said to be either true or false. Questions, proposals, suggestions, commands, and exclamations usually cannot, and so are not usually classified as statements. The following sentences are not statements:
Where is Khartoum? (question)
Let’s go to a movie tonight. (proposal) I suggest you get contact lenses. (suggestion) Turn off the TV right now. (command) Fantastic! (exclamation)
The statements that make up an argument are divided into one or more premises and exactly one conclusion. The premises are the statements that set forth the reasons or evidence, and the conclusion is the statement that the evidence is claimed to support or imply. In other words, the conclusion is the statement that is claimed to follow from the premises. Here is an example of an argument:
All film stars are celebrities.
Halle Berry is a film star. Therefore, Halle Berry is a celebrity.
The first two statements are the premises; the third is the conclusion. (The claim that the premises support or imply the conclusion is indicated by the word “therefore.”) In this argument the premises really do support the conclusion, and so the argument is a good one. But consider this argument:
Some film stars are men.
Cameron Diaz is a film star. Therefore, Cameron Diaz is a man.
In this argument the premises do not support the conclusion, even though they are claimed to, and so the argument is not a good one.
One of the most important tasks in the analysis of arguments is being able to distinguish premises from conclusions. If what is thought to be a conclusion is really a premise, and vice versa, the subsequent analysis cannot possibly be correct. Many arguments contain indicator words that provide clues in identifying premises and conclusion. Some typical conclusion indicators are therefore accordingly entails that wherefore we may conclude hence thus it must be that it follows that consequently for this reason implies that we may infer so as a result
Whenever a statement follows one of these indicators, it can usually be identified as the conclusion. By process of elimination the other statements in the argument are the premises. Example:
Tortured prisoners will say anything just to relieve the pain. Consequently, torture is not a reliable method of interrogation.
The conclusion of this argument is “Torture is not a reliable method of interrogation,” and the premise is “Tortured prisoners will say anything just to relieve the pain.”
If an argument does not contain a conclusion indicator, it may contain a premise indicator. Some typical premise indicators are since in that seeing that as indicated by may be inferred from for the reason that because as in as much as for given that owing to Any statement following one of these indicators can usually be identified as a premise. Example:
Expectant mothers should never use recreational drugs, since the use of these drugs can jeopardize the development of the fetus.
The premise of this argument is “The use of these drugs can jeopardize the development of the fetus,” and the conclusion is “Expectant mothers should never use recreational drugs.”
In reviewing the list of indicators, note that “for this reason” is a conclusion indicator, whereas “for the reason that” is a premise indicator. “For this reason” (except when followed by a colon) means for the reason (premise) that was just given, so what follows is the conclusion. On the other hand, “for the reason that” announces that a premise is about to be stated.
Sometimes a single indicator can be used to identify more than one premise. Consider the following argument:
It is vitally important that wilderness areas be preserved, for wilderness provides essential habitat for wildlife, including endangered species, and it is a natural retreat from the stress of daily life.
The premise indicator “for” goes with both “Wilderness provides essential habitat for wildlife, including endangered species,” and “It is a natural retreat from the stress of daily life.” These are the premises. By method of elimination, “It is vitally important that wilderness areas be preserved” is the conclusion.
Some arguments contain no indicators. With these, the reader/listener must ask such questions as: What single statement is claimed (implicitly) to follow from the others? What is the arguer trying to prove? What is the main point in the passage? The answers to these questions should point to the conclusion. Example:
The space program deserves increased expenditures in the years ahead. Not only does the national defense depend on it, but the program will more than pay for itself in terms of technological spin-offs. Furthermore, at current funding levels the program cannot fulfill its anticipated potential.
The conclusion of this argument is the first statement, and all of the other statements are premises. The argument illustrates the pattern found in most arguments that lack indicator words: The intended conclusion is stated first, and the remaining statements are then offered in support of this first statement. When the argument is restructured according to logical principles, however, the conclusion is always listed after the premises:
P1: The national defense is dependent on the space program.
P2: The space program will more than pay for itself in terms of technological spinoffs.
P3: At current funding levels the space program cannot fulfill its anticipated potential.
C: The space program deserves increased expenditures in the years ahead.
When restructuring arguments such as this, one should remain as close as possible to the original version, while at the same time attending to the requirement that premises and conclusion be complete sentences that are meaningful in the order in which they are listed.
Note that the first two premises are included within the scope of a single sentence in the original argument. For the purposes of this chapter, compound arrangements of statements in which the various components are all claimed to be true will be considered as separate statements.
Passages that contain arguments sometimes contain statements that are neither premises nor conclusions. Only statements that are actually intended to support the conclusion should be included in the list of premises. If, for example, a statement serves merely to introduce the general topic, or merely makes a passing comment, it should not be taken as part of the argument. Examples:
The claim is often made that malpractice lawsuits drive up the cost of health care. But if such suits were outlawed or severely restricted, then patients would have no means of recovery for injuries caused by negligent doctors. Hence, the availability of malpractice litigation should be maintained intact.
Massive federal deficits push up interest rates for everyone. Servicing the debt gobbles up a huge portion of the federal budget, which lowers our standard of living. And big deficits also weaken the value of the dollar. For these reasons, Congress must make a determined effort to cut overall spending and raise taxes. Politicians who ignore this reality imperil the future of the nation.
In the first argument, the opening statement serves merely to introduce the topic, so it is not part of the argument. The premise is the second statement, and the conclusion is the last statement. In the second argument, the final statement merely makes a passing comment, so it is not part of the argument. The premises are the first three statements, and the statement following “for these reasons” is the conclusion.
Closely related to the concepts of argument and statement are those of inference and proposition. An inference, in the narrow sense of the term, is the reasoning process expressed by an argument. In the broad sense of the term, “inference” is used interchangeably with “argument.” Analogously, a proposition, in the narrow sense, is the meaning or information content of a statement. For the purposes of this book, however, “proposition” and “statement” are used interchangeably.
Note on the History of Logic
The person who is generally credited as the father of logic is the ancient Greek philosopher Aristotle (384–322 b.c.). Aristotle’s predecessors had been interested in the art of constructing persuasive arguments and in techniques for refuting the arguments of others, but it was Aristotle who first devised systematic criteria for analyzing and evaluating arguments.
Aristotle’s chief accomplishment is called syllogistic logic, a kind of logic in which the fundamental elements are terms, and arguments are evaluated as good or bad depending on how the terms are arranged in the argument. Chapters 4 and 5 of this textbook are devoted mainly to syllogistic logic. But Aristotle also deserves credit for originating modal logic, a kind of logic that involves such concepts as possibility, necessity, belief, and doubt. In addition, Aristotle catalogued several informal fallacies, a topic treated in Chapter 3 of this book.
After Aristotle’s death, another Greek philosopher, Chrysippus (280–206 b.c.), one of the founders of the Stoic school, developed a logic in which the fundamental elements were whole propositions. Chrysippus treated every proposition as either true or false and developed rules for determining the truth or falsity of compound propositions
from the truth or falsity of their components. In the course of doing so, he laid the foundation for the truth functional interpretation of the logical connectives presented in Chapter 6 of this book and introduced the notion of natural deduction, treated in Chapter 7.
For thirteen hundred years after the death of Chrysippus, relatively little creative work was done in logic. The physician Galen (a.d. 129–ca. 199) developed the theory of the compound categorical syllogism, but for the most part philosophers confined themselves to writing commentaries on the works of Aristotle and Chrysippus. Boethius (ca. 480–524) is a noteworthy example.
The first major logician of the Middle Ages was Peter Abelard (1079–1142). Abelard reconstructed and refined the logic of Aristotle and Chrysippus as communicated by Boethius, and he originated a theory of universals that traced the universal character of general terms to concepts in the mind rather than to “natures” existing outside the mind, as Aristotle had held. In addition, Abelard distinguished arguments that are valid because of their form from those that are valid because of their content, but he held that only formal validity is the “perfect” or conclusive variety. This textbook follows Abelard on this point.
After Abelard, the study of logic during the Middle Ages flourished through the work of numerous philosophers. A logical treatise by William of Sherwood (ca. 1200–1271) contains the first expression of the “Barbara, Celarent . . .” poem quoted in Section 5.1 of this book, and the Summulae Logicales of Peter of Spain (ca. 1205–1277) became the standard textbook in logic for three hundred years. However, the most original contributions from this period were made by William of Ockham (ca. 1285–1347). Ockham extended the theory of modal logic, conducted an exhaustive study of the forms of valid and invalid syllogisms, and further developed the idea of a metalanguage, a higher-level language used to discuss linguistic entities such as words, terms, and propositions.
Toward the middle of the fifteenth century, a reaction set in against the logic of the Middle Ages. Rhetoric largely displaced logic as the primary focus of attention; the logic of Chrysippus, which had already begun to lose its unique identity in the Middle Ages, was ignored altogether, and the logic of Aristotle was studied only in highly simplistic presentations. A reawakening did not occur until two hundred years later through the work of Gottfried Wilhelm Leibniz (1646–1716).
Leibniz, a genius in numerous fields, attempted to develop a symbolic language or “calculus” that could be used to settle all forms of disputes, whether in theology, philosophy, or international relations. As a result of this work, Leibniz is sometimes credited with being the father of symbolic logic. Leibniz’s efforts to symbolize logic were carried into the nineteenth century by Bernard Bolzano (1781–1848).
In the middle of the nineteenth century, logic commenced an extremely rapid period of development that has continued to this day. Work in symbolic logic was done by many philosophers and mathematicians, including Augustus De Morgan (1806–1871), George Boole (1815–1864), William Stanley Jevons (1835–1882), and John Venn (1834–1923). The rule bearing De Morgan’s name is used in Chapter 7 of this book. Boole’s interpretation of categorical propositions and Venn’s method for diagramming
them are covered in Chapters 4 and 5. At the same time a revival in inductive logic was initiated by the British philosopher John Stuart Mill (1806–1873), whose methods of induction are presented in Chapter 10.
Across the Atlantic, the American philosopher Charles Sanders Peirce (1839–1914) developed a logic of relations, invented symbolic quantifiers, and suggested the truth-table method for formulas in propositional logic. These topics are covered in Chapters 6 and 8 of this book. The truth-table method was completed independently by Emil Post (1897–1954) and Ludwig Wittgenstein (1889–1951).
Toward the end of the nineteenth century, the foundations of modern mathematical logic were laid by Gottlob Frege (1848–1925). His Begriffsschrift sets forth the theory of quantification presented in Chapter 8 of this text. Frege’s work was continued into the twentieth century by Alfred North Whitehead (1861–1947) and Bertrand Russell (1872–1970), whose monumental Principia Mathematica attempted to reduce the whole of pure mathematics to logic. The Principia is the source of much of the symbolism that appears in Chapters 6, 7, and 8 of this text.
During the twentieth century, much of the work in logic has focused on the formalization of logical systems and on questions dealing with the completeness and consistency of such systems. A now-famous theorem proved by Kurt Gödel (1906–1978) states that in any formal system adequate for number theory there exists an undecidable formula—that is, a formula such that neither it nor its negation is derivable from the axioms of the system. Other developments include multivalued logics and the formalization of modal logic. Most recently, logic has made a major contribution to technology by providing the conceptual foundation for the electronic circuitry of digital computers.
eXercise 1.1
I. Each of the following passages contains a single argument. Using the letters “P” and “C,” identify the premises and conclusion of each argument, writing premises first and conclusion last. List the premises in the order in which they make the most sense (usually the order in which they occur), and write both premises and conclusion in the form of separate declarative sentences. Indicator words may be eliminated once premises and conclusion have been appropriately labeled. The exercises marked with a star are answered in the back of the book.
★1. Carbon monoxide molecules happen to be just the right size and shape, and happen to have just the right chemical properties, to fit neatly into cavities within hemoglobin molecules in blood that are normally reserved for oxygen molecules. Consequently, carbon monoxide diminishes the oxygen-carrying capacity of blood.
(Nivaldo J. Tro, Chemistry: A Molecular Approach, 2nd ed.)
2. Since the good, according to Plato, is that which furthers a person’s real interests, it follows that in any given case when the good is known, men will seek it. (Avrum Stroll and Richard Popkin, Philosophy and the Human Spirit)
★
3. As the denial or perversion of justice by the sentences of courts, as well as in any other manner, is with reason classed among the just causes of war, it will follow that the federal judiciary ought to have cognizance of all causes in which the citizens of other countries are concerned.
(Alexander Hamilton, Federalist Papers, No. 80)
4. When individuals voluntarily abandon property, they forfeit any expectation of privacy in it that they might have had. Therefore, a warrantless search or seizure of abandoned property is not unreasonable under the Fourth Amendment.
( Judge Stephanie Kulp Seymour, United States v. Jones)
5. Artists and poets look at the world and seek relationships and order. But they translate their ideas to canvas, or to marble, or into poetic images. Scientists try to find relationships between different objects and events. To express the order they find, they create hypotheses and theories. Thus the great scientific theories are easily compared to great art and great literature.
(Douglas C. Giancoli, The Ideas of Physics, 3rd ed.)
6. The fact that there was never a land bridge between Australia and mainland Asia is evidenced by the fact that the animal species in the two areas are very different. Asian placental mammals and Australian marsupial mammals have not been in contact in the last several million years.
( T. Douglas Price and Gary M. Feinman, Images of the Past)
★7. It really does matter if you get enough sleep. We need sleep to think clearly, react quickly, and create memories. Studies show that people who are taught mentally challenging tasks do better after a good night’s sleep. Other research suggests that sleep is needed for creative problem solving.
(U.S. National Institutes of Health, “Your Guide to Healthy Sleep”)
8. The classroom teacher is crucial to the development and academic success of the average student, and administrators simply are ancillary to this effort. For this reason, classroom teachers ought to be paid at least the equivalent of administrators at all levels, including the superintendent.
(Peter F. Falstrup, letter to the editor)
9. An agreement cannot bind unless both parties to the agreement know what they are doing and freely choose to do it. This implies that the seller who intends to enter a contract with a customer has a duty to disclose exactly what the customer is buying and what the terms of the sale are.
(Manuel G. Velasquez, “The Ethics of Consumer Production”)
★10. Punishment, when speedy and specific, may suppress undesirable behavior, but it cannot teach or encourage desirable alternatives. Therefore, it is crucial to use positive techniques to model and reinforce appropriate behavior that the person can use in place of the unacceptable response that has to be suppressed.
( Walter Mischel and Harriet Mischel, Essentials of Psychology)
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with a jerk, seeking to arrive at a part more palatable. When thus engaged in feeding, and particularly when playfully pursuing the hen among the twigs, his bright yellow coat glows beautifully through the openings of the green leaves.
I have observed so frequently as to be worthy of notice, that when shot, the Banana bird grasps the twig on which he was sitting, so tenaciously as to hang from it, body downwards, until death at length relaxes the clasp.
The nest of this bird is an interesting structure; like that of the Baltimore of the Northern continent, it is a deep purse suspended from two parallel twigs, or from a fork. One before me is composed chiefly of the wiry fibres plucked from the fronds of the Palmettothatch, with some horse-hair interwoven. Sometimes, where thatchthreads are scarce, horse-hair alone is used, and the structure is particularly neat. But the more ordinary material is a vegetable substance, so closely resembling horse-hair, even on a minute inspection, that I have had difficulty in persuading intelligent persons that it was not actual hair, till I applied it to the flame of a candle, when it burnt without shrivelling. But I am very uncertain what the substance is; some say it is the Tillandsia usneoides or “Old man’s beard,” a very common tree-parasite, but it assuredly is not this; I have suspected it to be the fibrous stem of the Dodder, dried; a nest newly made, I observed to be of the bright buff hue of that plant, whence I presumed that the stems are sometimes taken in a recent, and even a growing state. A friend tells me, that he has, with much gratification, watched the process of building. The hairs or threads are procured one by one, and carried to the selected spot, where they are deposited in a loose heap. From this accumulated mass of material, the work is carried on, and progresses rapidly, when once begun. When a few threads are laid and interlaced for the base, the work becomes perceptible and interesting. Both birds work together; one taking a thread, and weaving-in one end, holds down the loose part with his beak; while his mate takes the ends of others projecting, and lays them tightly down over it, interweaving them with others. Other threads are crossed in the same manner, in every
direction, until a slight but very compact purse is made, resembling a loose cloth. As it hangs, the texture is so thin, that a person below can discern the eggs or young within. Four eggs are laid, pointed at the less end: they are white, marked with a few angular scratches, and large spots of deep brown, and measure 1 inch by ⁷⁄₁₀. If an intruder attempt to rifle the nest when the young are there, both old birds fly round in excessive perturbation, and cry TomPaine’spick-aninny, with vociferous shrillness.
In March I have dissected females, which displayed a brilliance of plumage, innowiseinferior to that of the male.
I presume this to be the Watchy-picketof Sloane.
Mr. Hill has mentioned to me two other species of Icterus, both black, the one larger, the other smaller, which have been found in the mountains near Kingston. I think I once saw the former in Mount Edgecumbe.
In ordinary seasons this well-known bird arrives in vast numbers from the United States, in the month of October, and scattering over the lowland plains, and slopes of the sea-side hills, assembles in the guinea-grass fields, in flocks amounting to five hundred or more. The seed is then ripe, and the black throngs settle down upon it, so
densely, that numbers may be killed at a random discharge. To procure the seed, the birds perch on the culm, but as the weight would bear down a single stalk, each grasps several culms in its foot, while it rifles the panicles. At this time, the males are dressed in the sober livery of the females. Early in November they depart for the southern continent, but during their brief stay they are in great request for the table. Dr. Chamberlaine only echoes the general estimation, when he says:—“The Butter-bird is a bonne bouche; it is but a mouthful, but a luscious and delightful one. Their note,” he adds, “during their migration hither, is simply ping,ping,ping:—what it may be in its native woods, I do not know. But wounded birds have been secured and kept in cages, and when placed in the same room with a Canary have soon acquired similar notes, and in time warble with equal strength and melody.” (Jam. Alm. 1840; p. 25.)
When the spring rains have set in, usually in the month of April, they again become our transient guests for a few days, on their northward migration, when the males are conspicuous in their nuptial dress. Other species of grass are now seeding, and the nutritive farinaceous grains of many neglected weeds afford them a supply during their brief sojourn.
FAM.—FRINGILLADÆ.—(The Finches.)
CASHEW-BIRD.[64]
Mountain Bulfinch(ROB.)—Orange-bird. TanagraZena.
Fringilla Zena, LINN.
Fringilla Bahamensis, BRISS.
Tanagra multicolor, VIEILL.
Spindalis bilineatus, JARD. and SELB.—Ill. Orn. n.s. pl. 9.
[64] Length 7¾ inches, expanse 13, flexure 3⁹⁄₁₀, tail 3¼, rictus ¹³⁄₂₀, tarsus 1, middle toe ¾. Intestinal canal, wide, but only 7 inches long: no cæca. Stomach, a thin, almost membranous sac.
Though not very numerous, this beautiful bird is well-known, being conspicuous from his brilliant colours. He is spread over the country, from the mountains of the interior, to the plains of the coast. Rather social, though perhaps attracted by a common cause, the abundance of food;—we may sometimes see a dozen or more scattered over a large bully-tree, from the twigs of which they hang in all positions, while they pick the berries. Its flight is rapid, and performed in long undulations: during flight, a low sibilant note is uttered; but it is usually a silent bird.
About Spanish Town, it is called the Orange-bird, not from its feeding on oranges, but from the resemblance of its plump and glowing breast, to that beautiful fruit, as it sits among the dark green foliage. It is also called the Goldfinch.
I shot a male in September, and wounding him only in the breast, picked him up, more frightened than hurt. I carried him home in my handkerchief, and put him into a large cage, where he soon became quite a favourite. From the very first he was fearless and lively, found the use of the perches immediately, and did not flutter or beat himself against the sides, though persons stood close to the cage. This was large enough to allow him a short flight; and as there were several perches inserted at various heights and distances into the sides, he spent a great deal of his time in leaping from one to the other, seeming to enjoy it much. Seeing this, I put in one or two more, which were no sooner ready than he took notice of them, stretching himself towards them, cautiously at first, as if doubtful whether they would bear him; soon, however, he ventured boldly, and then took them regularly in his course. He always slept on the highest perch, with his head behind his wing. He was in full plumage, and his gay breast, and the fine contrasts of his striped head and wings, showed him off to advantage. I knew nothing that he would eat, save the berries of the bully-tree, none of which grew within a considerable distance. I first tried him with a few insects,
and small earthworms, but he took no notice of these: then I gathered a few bunches of fiddle-wood berries, which I had no sooner stuck into his cage than I was pleased to see him hop towards them, and pick off the ripe ones with much relish and discrimination. I was informed that in a wild state, he sometimes eats the sour-sop; as I had none of this fruit at hand, I gave him pieces of a ripe custard-apple and of a guava. He immediately began to eat of each, plucking off portions of the pulp, and also taking up the fleshy ovaria of which the former is composed, which he chewed with his beak till the enclosed seed was pressed out. But all these were forsaken so soon as I presented to him bunches of ripe pimento, black and sweet. These he picked off greedily, masticating each in the beak, until the seeds, which I suppose, were too hotly aromatic for his taste, fell out. It was amusing to see the persevering efforts he made to obtain those berries, which happened to be a little beyond his reach. He would jump from perch to perch impatiently, gazing with outstretched neck at the tempting fruit, then jump, and look again; then reach forward to them, until in the endeavour, he would overbalance himself, and perform an involuntary somerset. Nothing daunted, however, he persevered until he ventured to do, what he had been several times on tiptoe to do, leap on the bunch itself; and this he continued to do, though with some failures, holding on in a scrambling way, now by a leaf, now by the berries themselves, until he had rifled the bunch of the ripest.
After I had kept him about a week, during which his liveliness and good temper had much attached him to me, though he made not the slightest effort at song, I took him out to cleanse the feathers of his breast from the dried blood that had flowed from his wound. I gently rubbed them with a soft wet sponge, but whether he took cold, or whether I irritated the wound, I know not; but on being returned to the cage, he instantly began to breathe asthmatically with open beak, apparently with pain; interrupted now and then by fits of coughing, which continued all night, and on the next morning he died. On dissection, I could not find that the shot had penetrated
the chest, but they were imbedded in the muscles of the forearm, and had broken the scapula.
A nest, reported to be of the Cashew bird, was brought me on the 18th of June, taken from a pimento tree. It was a thick, circular mat, slightly concave, of a loose but soft texture, principally composed of cotton, decayed leaves, epidermis of weeds, slender stalks, and tendrils of passion-flower, intermingled, but scarcely interwoven. I think it probable that this had been sustained by a firmer framework; and that the person who took it merely tore out the soft lining as a bed on which the eggs might be carried. The child who brought it, could give no account of this. The eggs were two, longoval, taper at the smaller end; 1¹⁄₁₀ inch by nearly ⁸⁄₁₀; white, sparingly dashed with irregular dusky spots, in a rude ring around the larger end. The embryo was at this time formed.
SCARLET TANAGER.
Pyrangarubra.
Tanagra rubra, LINN.—Aud. pl. 354.
Pyranga rubra, VIEILL.
Of this gay-plumaged stranger, a male and female were seen in March of the present year, in that wild and magnificent gorge, called the Boca-guas, near Spanish Town. The brilliant appearance of the male, attracted the admiration of passers by, and he was at length shot, and brought to Mr. Hill.
About three weeks after this, a male, also in summer dress, occurred to my own observation, hopping about the small fruit-trees, on the banks of Bluefields River. He was very fearless, allowing me to sit and watch him within half-pistol-shot; now and then he flew down to the ground, by the side of the water, and remained a few moments peeping about; then he would fly up into a shrub, and
presently be down again to drink; for the season was parched with drought. I watched him full half an hour, before he flew away.
Both these instances show that the Scarlet Tanager, occasionally at least, takes our lovely island, in his spring migration from Central America to the north. He certainly does not winter with us, having been until this season unknown to Mr. Hill, who for many years has paid close attention to the migrant birds. Yet D’Orbigny states, that it winters in Cuba; perhaps, however, but casually.
Male. Irides bright hazel; beak and feet black. General plumage rather dull blue; throat deep rufous, cheeks black. Wing-quills and tail-feathers blackish with blue edges.
Female. Head and neck greenish grey: back olive brown: tertiaries and their coverts, and tail dark umber; the former with pale edges. Under parts ashy, approaching to white on the medial line of the belly.
The tongue of this species, pencilled and barbed at the tip, might give it a place among the Honey-suckers. It does not climb, however, nor cling by its feet, but perches. It is not a very common bird in the lowlands; but in the mountains I have found it rather plentiful. It frequents berry-bearing trees of various species, in small parties,
with no very strong sociality; its only note is a single chirp, sharp and shrill. Towards the end of the year, when the dark and glossy foliage of the orange groves is relieved by the profuse golden fruit, reminding the beholder, of the fabled gardens of the Hesperides, this Tanager becomes numerous, hopping about the twigs, and pecking holes in the ripe fruit. Many are then readily caught by smearing the twigs in the vicinity of a half-eaten orange, with bird lime, or “gum,” as it is called, the inspissated milk that exudes from an unripe naseberry. Females seem to predominate in these foraging parties, in the proportion of two or three to one; unless the young males have the same livery as their mothers.
Near the Hallow-well at Content, on a bush whose glossy black berries have obtained for it the name of wildpimento, but which is better known as rod-wood, we found a nest of the Orange Quit, in June. It was a very deep cup, of a coarse texture, rather rudely formed of blades of grass, and the leaves of Olyra latifolia, interwoven with stalks of grass. It was built on a horizontal branch, at the divergence of two twigs, but did not embrace them. Four small eggs, ¹³⁄₂₀ inch by ⁵⁄₁₀, contained at that time embryos half matured: they were white, splashed with dull red, thinly, except at the larger end, where the spots were numerous and confluent. The male probably assists in incubation; for he was seen to emerge from the nest.
Euphonia Jamaica, DESM.
Grey Grosbeak, BROWN.—Ill. Zool. pl. 26.
BLUE QUIT.[66]
EuphoniaJamaica.
Fringilla Jamaica, LINN.
[66] Length 4½ inches, expanse 8, flexure 2⁶⁄₁₀, tail 1⁵⁄₁₀, rictus ⁵⁄₁₀, tarsus ¾, middle toe ¹¹⁄₂₀. Irides deep hazel: feet dark grey; beak grey, the fissure, ridge and tip black.
Male. Upper parts slate blue, glossy, more or less tinged on the rump with green. Throat, breast, and sides pale grey: belly yellow; under tail coverts greyish white. The blue on the wing-quills nearly black.
Female. Loins, upper tail-coverts, and thighs, yellow-green; no yellow on the belly. Otherwise as the male.
A short stumpy bird, and rather inelegant from the shortness of its tail, the Blue Quit reminds me of the Nut-hatches. It is very common about homesteads, where it frequents fruit-trees, particularly the sops: it is, however, nowise infrequent in the woods, both on the mountains and in the lowlands. It hops busily about the twigs and fruits, picking in any position, back or belly, head or tail, uppermost. When the sour-sop is ripe, they flock to it in such numbers, that the tree appears covered with them: the negro children then set limed twigs for them, and I have had them brought to me thus as fast as they could be taken down. The boys cut diagonal notches into the bark of a naseberry tree, (Achras), or score an unripe fruit; a white milk exudes, so abundant as to drop quickly, and is caught on a leaf. At first it has the consistence of thin cream, but half an hour’s exposure thickens it, and gives it tenacity enough to be drawn into threads; when they consider it “ripe.” A twig smeared with this “gum,” is stuck into the half-eaten sour-sop or custard-apple, presenting a very inviting perch to the hungry birds. One soon hops on the fatal twig, and is in an instant fluttering helplessly, fast at the feet. Banana birds, Mocking birds, and Cashew birds are also taken in this way. The appearance of the intestinal viscera at such a season, is very singular, being distended with the white pulp throughout their length, perfectly visible from the transparency of the intestines. At first the stomach seems to be wanting, and this much surprised me; but the fact is, that organ is simply a thin membranous sac, or rather canal, differing in no apparent respect from the intestine, save in slightly increased capacity.
The musical powers of our little Blue Quit are considerable: it is a sweet and constant song-bird. It has various notes; frequently it chirps pertinaciously, like the Humming birds; at other times it utters a long “twee,” like the Chicken-Hawk; sometimes it delights in a soft warbling repetition of a single note; sometimes its voice is closely like the plaintive mewing of a kitten. But besides these it has a real song, sweet and musical. In March at Spanish Town, I heard two, apparently both males, warbling close together on a genip-tree opposite my window, very sweetly but hurriedly. When one flew to another twig the other presently followed. By and bye they ceased that melody, and one took to a strain consisting of about a dozen rapid repetitions of the same note, ending with one elevated note, with a jerking abruptness. This strain he repeated several times.
About the middle of April, a pair of Blue Quits built a nest on one of the topmost branches of a high fiddle wood in the yard of Bluefields house. The tree was much infested with that parasite called Old man’s beard, large bunches of which grew on most of the limbs and boughs, so numerously as to touch each other in long successions. Two of these contiguous bunches the birds had managed to separate, either by picking away portions, or by pushing them apart, so as to open a large hollow, and in this they built a very snug domed nest. It was globular in form, about as large as an infant’s head, with an opening in one side, composed of dry grass, the dried stems of the Tillandsia, tendrils of passion-flower, bits of rag, profusely intermixed with cotton and the down of plants; yet these soft substances were not used to line the structure, the grass only appearing in the inside. Perhaps it was not finished, for the birds were passing in and out, and thus betrayed its existence, for so identified was it in appearance with the bunches around, that but for this ingress and egress, and the little opening, I could not have detected it. I sent up a lad to examine it, but in so doing, he partially broke the branch, causing it to hang down; and this I presume awakened suspicion, for the birds deserted it, and in a few days I had it taken down. It was empty.
