The sheer amount of information available to today’s psychology student, and the ease with which that information can be obtained, is greater than it has ever been in the past. Though this is no doubt a blessing, it is not without its dangers. In particular, it is easy for the student to become bogged down in a mass of facts and details with little appreciation of how everything fits together. Knowing disjointed facts, no matter how vast that knowledge may be, does not constitute understanding. It is only when that knowledge is embedded within an overarching framework that understanding occurs. Knowledge of the historical and philosophical foundationsofpsychologyprovidessuchaframework.
But in order to achieve this, the historical and philosophical foundations of psychology cannot themselves be presented in a bitty and disjointed fashion. There must be some sort of narrative, not just a bunch of ideas and theories. There must be an indication of how ideas fit together, and of the pervasive influence of certain core ideas that resurface at various points throughout the history of psychology. That is what I have tried to do in this book.
This book grew out of a course on the history and philosophy of psychology that I taught at the University of Manchester. In preparing the course I had difficulty in finding a book that tied together the ideas and theories in quite the way I wanted. I felt that many of the available textbooks were repositories of factual information – useful factual information, no doubt – but that they did not present a coherent narrative. I also thought that there was a tendency to try to cover too much ground, too many thinkers, and that, as a result, the treatment of them was often a little cursory. My goal, then, was to provide more of a coherent narrative, and to discusstheideaspresentedingreaterdepth.
The book is perhaps more selective than some others on the history and philosophy of psychology. I make no claims to its being comprehensive –nearly everyone will be able to point out some favourite psychologist or
philosopher who has not been included or has not been given enough attention. But I thought it better to look in more detail at the work of a smaller selection of thinkers than to deal superficially with a large number of thinkers. It is also the case that concentrating on a smaller number of thinkers makes it easier to grasp the interconnections between their ideas than if one were to try to cover everyone of importance. I believe that, after havingread this book, students will be equipped to locate the ideas of other thinkers not discussed in the book within the general framework that it provides.
The narrative presented in this book is, then, not the only story that could be told about the historical and philosophical foundations of psychology. It does, however, deal with what I believe to be some of the most important and recurring problems and issues concerning the foundations of psychology – issues such as the mind–body problem, the extent to which the mind itself constructs our experience, and the extent to which mental processes can be understood as being purely internal to the organism or essentially connected to the environment. These fundamental issues, and others like them, reappear throughout the book. These issues are discussed in relation to the thought of major philosophers, such as Descartes, Locke, Hume, and Kant, as well as the ideas of influential psychologists, such as William James and Wilhelm Wundt, and psychological movements, such as Gestaltpsychologyandbehaviourism.
The book is organised in a roughly chronological order. It is sometimes the case that books on the history of ideas are organised around themes, but a chronological presentation seemed to me to be the most natural one for providingthenarrativethatIdesired.
Featuresofthebook
Thebook,asmentionedabove,grewoutofmyundergraduateteaching,and so is aimed at undergraduate psychology students, though I hope that postgraduate students would also find something of value in it. I have tried to write the book as clearly as possible, but it is inevitable that some technical terms will feature in the text. Where these occur, they are printed inboldandaredefinedinaglossaryattheendofthebook.
To give the student some feel for the personal context in which ideas originated, I have included, in separate boxes, biographical information on the main thinkers discussed in the text. In addition to this, timelines at the beginning of each chapter relate the work of the thinkers discussed in that chapter to other historical events that were occurring at the same time. The studentwillalsofindrevisionquestionsattheendofeachchapter.
Acknowledgements
I would like to thank the anonymous reviewers of draft chapters of this book, and Hetty Marx, Valerie Appleby, and Raihanah Begum of Cambridge University Press for all their help in helping me knock the book into shape. The book would have been a poorer one if it were not for their suggestions. Thanks are also due to my friend and colleague Professor Ivan Leudar, with whom I taught the course on which this book is based, for his constant encouragement. The biggest thanks of all go to my partner, Donna Lloyd,foralltheloveandsupportIcouldhavewishedfor.
PartI Philosophyofscience
1 LogicalpositivismandPopper’sfalsificationism
I have chosen to start this survey of the historical and philosophical foundations of psychology with an examination of some of the major theories put forward in the philosophy of science. This might, at first sight, seemtobearatherunnaturalplacetostart,buttherearegoodreasonsforit. Firstly, given that most psychologists think of their discipline as a science and of themselves as scientists, it is important to investigate ideas about what science actually is and what, if anything, are the characteristics that differentiateitfromother,non-scientific,intellectualdisciplines.
But there is another reason for looking at the philosophy of science to start off with, and that is that there is a good deal of overlap between ideas in the philosophy of science and psychology. Both the philosophy of science and psychology are concerned, at least in part, with the question of how we know about the world. As we shall see, many of the themes that will arise inthe course ofthis presentation ofthe philosophy ofscience will re-emerge later in the history of psychology. Indeed, all of the philosophers of science that will be discussed in these three chapters make use of psychologicalideasaboutthenatureofknowledge.
One particularly influential view of human knowledge goes, roughly, like this:wegainknowledgeoftheworldthroughthesenses;eventsandobjects intheworldimpingeonoursenseorgans,andthebasicsensoryinformation that they thereby transmit is the basis on which our knowledge of the world stands. This view has its counterpart in the philosophy of science in the theory that scientific knowledge is built up from observations of things and eventsinthenaturalworld.Accordingtothisview,observationalfactsform thebasisonwhichscientificknowledgestands.
These two views go hand in hand, and they are rejected by Karl Popper, the first philosopher of science that we are going to cover. He referred, dismissively, to the view of knowledge that has just been sketched as ‘the bucket theory of knowledge’ because it envisages the human mind as a sort of receptacle for factual information acquired via the senses. This view is also rejected by the three other major philosophers of science to be covered in these chapters: Thomas Kuhn, Imre Lakatos, and Paul Feyerabend. Though they disagree strongly with Popper on other matters, all agree that the bucket theory of mind gives an erroneous picture not only of scientific knowledge,butofhumanknowledgeingeneral.
The bucket theory is traced by Popper, with some justification, to a schoolofphilosophycalledempiricism. This school of thought emphasises the importance of experience, and particularly sensory or perceptual experience, in gaining knowledge about the world. It is particularly associated with philosophers such as John Locke and David Hume, whose ideas we will consider in more detail in Chapters5 and 6. According to the empiricists, the basic perceptual information that is provided by the senses is transformed into more elaborate knowledge through association: the different isolated bits of factual information become associated with one another, they become bound together, so as to create from a disconnected array of facts a coherent network of interconnected pieces of information. This idea of learning through association was to have great influence on the behaviourists (see Chapter 16). Again, this general view of human knowledge has its counterpart in the philosophy of science. According to the empiricist view of science, scientific theories are created by joining together the isolated facts and observations that scientists collect in the courseoftheirresearch.
Empiricism assumes that the basic observations and facts that are the foundation of science are given to the scientist. The scientist has only to observe nature to be provided with the building blocks of scientific knowledge and these observations will be all the more accurate the less the scientist’s mind is filled with expectations about what will be observed. Approaching the task of observing nature with pre-existing ideas about whatoneisgoingtofindis,accordingtotheempiricistapproachtoscience, likely to bias or distort one’s observations. The scientific ideal, then, is the completely open-minded and passive recipient of incoming information. It is only subsequent to having received this information that the mind can start to take an active role in the creation of scientific knowledge, by combining, associating, abstracting, and generalising ideas on the basis of the sure information provided by the unbiased operation of the senses. The bricksare given bynature;thebuildingisconstructedbymind.
The idea that science starts with the neutral observation of facts given to observation goes back to one of the earliest empiricists and thinkers on scientific method, Francis Bacon (1561–1626) (see Figure 1.1). For Bacon, the most important early step in scientific investigation was to remove from one’s mind all pre-existing beliefs and expectations so that one can, as a
scientist, make careful and unprejudiced observations of what one really sees, observations that are pure and uncontaminated. Bacon called the traditional or accepted beliefs that the scientist had to discard ‘the idols of the tribe’, and he was in no doubt that these idols had to be destroyed because they blocked the advance of scientific knowledge. The mind of the observer becomes cleansed and approaches as closely as possible to the blank slate on which empiricists believed nature could write its message unhindered. This purging of pre-existing beliefs and expectations has been likened by Lakatos (in his ‘Falsification and the methodology of scientific research programmes’; see Chapter 3) to a sort of psychotherapy that the empiricist believes is necessary to prepare one’s mind to receive the messageofnature.
The four philosophers of science to be discussed in these chapters all reject the empiricist view of science. In its place they put forward an
Fig.1.1 FrancisBacon
alternative view of science according to which the scientist is an active seeker of observations, not just a passive receiver. The scientist is not devoid of expectations or preconceptions, but, on the contrary, makes observations precisely in order to see whether these expectations are fulfilled. But the views of Popper, Kuhn, Lakatos, and Feyerabend go further than this. They assert that not only do a scientist’s preconceptions guide her search for observations, but that they play an active role in actuallystructuringtheobservationsthemselves.
This alternative to the empiricist view of science has its roots in an alternative view of human knowledge and perception, which can be traced to the ideas of Immanuel Kant (1724–1804). According to Kant, whose ideas will be discussed in more detail in Chapter 6, the human mind does not passively record sensory impressions, but has a hand in constituting and constructing those impressions from the outset of perception itself. In particular, argued Kant, the mind has an innate structure, a built-in framework,throughwhichwemakesenseoftheworldaroundus.Themost obvious example of this is the physiology of the sensory apparatus itself –we can only hear a limited range of sounds or see a limited range of light frequencies. Thus, even our most basic perceptions are determined not only by what is out there in the external world, but by the form of our own minds.ThisfundamentalKantianinsightformedthebasicpresuppositionof psychologistssuchasWundt(seeChapter11).
The physiology of the perceptual systems is, however, not the only influence on the way that the mind structures perceptual experience. Another influence is the cultural experience of the perceiver, and it is on this factor that philosophers of science have focused. This, unlike the physiology of the perceptual systems, is not fixed, but can change as a result of learning. Popper, Kuhn, Lakatos, and Feyerabend all in their own waysarguethat,justastheeducationandtrainingofaliteratepersonallows her to see lines and squiggles on a page as meaningful words, so the education and training of a scientist structures her observations in particular ways. The expert naturalist has learned to see specific species of birds where the non-expert sees just undifferentiated ‘birds’; the trained astronomerhas learned toseetheconstellationswhereasthenon-expertjust sees ‘stars’. Contrary to empiricism, it is not just the edifice of knowledge
The empiricist view of science against which much of twentieth-century philosophy of science defined itself was given its most influential modern formulation in a school of thought called logical positivism. Logical positivism is particularly associated with a loose grouping of scientists and philosophers who worked in Vienna in the 1920s and 1930s, but was also promoted by English philosophers such as A. J. Ayer (1910–89). In order fully to understand the work of Popper and later philosophers of science it isuseful,firstofall,tounderstandwhattheywerereactingagainst.
The logical positivists were particularly concerned with the question of what it is that makes a statement meaningful. They were concerned with this because they believed that a great deal of philosophy was nothing more than empty verbiage, high-sounding rhetoric that did not mean anything. This sort of grandiose philosophical jargon they dismissed as mere ‘metaphysics’. To be truly rigorous in our thoughts, argued the logical positivists, we have to have some criterion that differentiates a truly meaningful statement from a superficially plausible one that does not have any meaning. We have to have some demarcation between sense and nonsense.
In trying to specify a criterion of meaning, the logical positivists took their lead from the eighteenth-century empiricist philosopher David Hume (whose ideas are discussed in more detail in Chapter6), who recommended thefollowingcourseofaction:
If we take in our hand any volume; of divinity or school metaphysics, for instance; let us ask, “Does it contain any abstract reasoning concerning quantity or number?” No. “Does it contain any experimental reasoning concerning matter of fact and existence?” No. Commit it then to the flames: for it can contain nothing but sophistry andillusion.
(Enquiries concerning Human Understanding and concerning the Principles of Morals,p.165)
For Hume, then, and for his latter-day followers among the logical positivists, anymeaningful statement mustfallintooneoftwocategories: it must either contain ‘abstract reasoning’ or ‘experimental reasoning’. The statements of mathematics would be examples of the first category of meaningful statement. ‘Squares have four sides’ or ‘The sum of the internal angles of a triangle is 180 degrees’ or ‘2 + 3 = 5’ are all meaningful statements, but note that they are not arrived at from observing actual states of affairs in the world. The general statement ‘Squares have four sides’ is not obtained by going around counting the sides of every square that one encounters and discovering that squares have four sides. Rather, we would say that squares have four sides by definition. If someone were to announce that he had found a ‘three-sided square’, we would not hail this as a mathematical breakthrough but as evidence that the person in question did not know the meaning of the term ‘square’. These mathematical statements are examples of logical truths. Logical truths are true in virtue of their structure and the definitions of the terms that they contain, not because they giveusaccurateinformationabouttheworld.Forexample,thestatement‘It is either raining or not raining outside my window’ is true – it really is either raining or not raining – but it gives no information as to what the weatherisactuallylike.
The second class of meaningful statements, according to Hume, consists of those statements containing ‘experimental reasoning concerning matter of fact’. In contrast to logical truths, statements of this second type do give us information about the way that the world actually is. They are observational statements. In contrast to ‘It is either raining or not raining outside my window’, the statement ‘It is raining outside my window’ is an empirical statement; it says that a certain state of affairs exists in the world. Itassertsafact.
Empiricalorobservationalstatements,unlikelogicaltruths,canbetrueor false, and we can check on their truth or falsity by actually making the relevant observations to see if the world actually is the way that the statement says that it is. We can, for example, look outside the window to see if it really is raining. If we see that the facts actually correspond to what the statement says, then we have verified the statement. An observation statement, then, is a statement that can, even if only in principle, be verified.
Ayermadethepointasfollows:
The criterion which we use to test the genuineness of apparent statements of fact is the criterion of verifiability. We say that a sentence is factually significant to any given person, if, and only if, he knowshowtoverifythepropositionwhichitpurportstoexpress–that is, if he knows what observations would lead him, under certain conditions, to accept the proposition as being true, or reject it as being false. If, on the other hand, the putative proposition is of such a character that the assumption of its truth, or falsehood, is consistent with any assumption whatsoever concerning the nature of his future experience, then, as far as he is concerned, it is, if not a tautology, a merepseudo-proposition.
(Language, Truth and Logic,p.16)
AyergoesontogiveaquotationfromtheEnglishphilosopherF.H.Bradley as an example of the sort of meaningless metaphysics that the logical positivistssoughttoexcisefromphilosophicaldiscourse:
such a metaphysical pseudo-proposition as ‘the Absolute enters into, but is itself incapable of, evolution and progress’, is not even in principle verifiable. For one cannot conceive of an observation which would enable one to determine whether the Absolute did, or did not, enterintoevolutionandprogress.
(Language, Truth and Logic,p.17)
We can conclude this section, then, by saying that, according to the logical positivists,forastatementtohaveanymeaningatallitmustfallintooneof these two classes: it must either be true as a matter of logic or it must be an observational statement that gives us verifiable information about the way that the world is. It is because of this emphasis on the verification of empirical statements that the logical positivists’ theory of meaning is sometimesreferredtoasverificationism.
Theproblemofinduction
We have seen in the earlier sections of this chapter that, from the empiricist viewpoint, all science starts with observations. The statements or propositions that convey these observations clearly fall into the second of the logical positivists’ two categories of meaningful statement: they assert the existence of some fact or facts about the world which can be verified by makingappropriateobservations.
But, though facts are important to science, science is not just a collection of facts. The scientist is not content with a large number of individual observations such as ‘steam was produced when a kettle of water was brought to boiling at 7.30 a.m. on 26th April 2013’. She does not just want to make statements about individual events, but wants to make general statements about whole classes of events: not just what happened when waterwasboiledthismorninginakitcheninManchester,butwhathappens when water boils in general. Something has to be done with the individual facts collected by the scientist to convert them from reports of particular events or things into general statements. Bacon believed that general patterns would somehow emerge from a large number of observations, but the logical positivists wanted to be more rigorous in identifying how this might happen. Specifying exactly how general scientific statements or laws are derived from individual observations was particularly important to the logical positivists because they believed that the meaningfulness of any scientificlawdependedonitsbeingbuiltfromverifiablefacts.
The process by which general conclusions are drawn from a number of individual observations is called induction, and it is here that, according to Popper, the whole programme of logical positivism foundered. To illustrate what is meant by induction or inductive reasoning it is useful to contrast it withdeductionor deductive reasoning.
Here is an example of deductive reasoning. We have the following two premises:
1. Alldairyproductsaremadefrommilk
2. Cheeseadairyproduct.
If we accept that these two premises are true, then they necessarily entail theconclusion‘Cheeseismadefrommilk.’
Here is another example of deductive reasoning. We have the following twopremises:
1. Allgreenthingsaremadefromgrass
2. Thecarpetisgreen.
If we accept that these two premises are true, then they necessarily entail theconclusion‘Thecarpetismadefromgrass.’
Bothoftheseareexamples ofvalidreasoning.Theyarevalidbecausethe conclusions follow from the premises as a matter of logical necessity. It so happens that in the second example the premises are not actually true, but the logical validity of the argument is concerned not with whether the premises and conclusions really are true are false, but whether the conclusion follows logically from the premises if, for the sake of argument, weacceptthemtobetrue.
In both of the above examples of deductive reasoning we move from general statements in the premises (e.g. ‘All dairy products are made from milk’)toconclusionsaboutparticularthings(e.g.cheeseasaparticulartype ofdairyproduct).Butthistypeofreasoning,whichgoesfromthegeneralto the particular, cannot be used to derive scientific theories or laws from observations, because in this case the argument has to go in the opposite direction.We start with individual, particular cases and from them arrive at generalconclusions.
It is here that we arrive at what is called the problem of induction, which was raised by Hume and then later used by Popper to undermine logical positivism. The problem of induction is simply that one cannot logically deriveageneralconclusionfromafinitenumberofindividualobservations. If, for example, one has tested 20, 30 or even 1000 participants in an experiment, it does not follow that all people will perform in this way. There is no way of knowing whether the 21st, 31st or 1001st participant mightperforminacompletelydifferentway.Wemight expect the21st,31st or 1001st participant to perform in broadly the same way as the preceding participants, but this is merely a subjective inclination rather than a logical necessity. For Popper, the invalidity of induction constituted a fatal flaw in the logical positivists’ programme of rigorously demonstrating how
scientific knowledge could be built on a foundation of observational statements.The
Box1.1 KarlPopper
Karl Raimund Popper was born in Vienna in 1902 to a middle-class family Though the family was Jewish in origin, both of his parents had converted to Protestantism before Popper was born. The atmosphere of the household was intellectual, and his parents were deeply interested in social and political issues as well as the arts and philosophy. Popper attended lectures in a variety of subjects – physics, mathematics, psychology, and philosophy – at the University of Vienna and later gained his doctorateinpsychology.Hewaskeenlyinterestedineducationandworkedforawhile as a social worker with deprived children and later as a teacher of mathematics and physics.
As a young man, Popper was active in left-wing politics and flirted with Marxism but later turned against it. His rejection of Marxism was, in part, prompted by the shooting dead of unarmed socialist demonstrators in Vienna by the police in 1919. Confronted by real bloodshed, Popper could no longer hope for the class war that the Marxists predicted and longed for He was also disturbed by the dogmatic nature of whathewassupposedtobelieveandwasconcernedthathehimselfhadacceptedthese doctrines in an uncritical manner Popper was also interested in the psychoanalytic ideasofFreudandAdler,butthesetoohecametosuspectofbeingdogmatic.
Following the annexation of Austria by the Nazis in 1936, Popper left for New Zealand. Though he had been raised in an ostensibly non-Jewish household, his grandparents were all Jewish, which meant that Popper himself would have been classifiedasJewishundertheNazis’raciallaws.ItwasinNewZealand,spurredonby the rise of totalitarianism in Europe, that Popper wrote his most influential political work, The Open Society and Its Enemies. In this work he argued in favour of liberal democracyandagainsttotalitarianismofbothleftandright.
At the end of World War II, Popper moved to England, where he worked at the London School of Economics and the University of London until his retirement in 1969 (see Figure1.2), although he continued to write right up until his death in 1994. Hewasknightedin1965.
Fig.1.2 KarlPopper
foundations themselves might be unassailable, but the construction of a theory upon them seemed to have no warrant in logic. Either the logical positivists’ picture of science was seriously wrong or the logic of science wascalledintoquestion.
Theroleoftheoryinobservation
Induction was not the only problem that Popper saw with logical positivism. For him the observations made by scientists were not firm and unassailable in the way that the logical positivists thought they were. Whereas the logical positivists had argued that we start with observation and end up with a theory, Popper argued that we cannot even make observations unless we already have a theory which guides those observations and makes sense of them. The whole empiricist picture of the open-minded scientist making completely neutral observations, her mind purged as completely as possible of any preconceptions or expectations, wasattackedbyPopperasnothingmorethanaperniciousmyth.
Popper (Conjectures and Refutations) recounted how he once asked a classroom of students to ‘observe’, and to write down their observations. The students were, not surprisingly, rather nonplussed by the vague instruction to‘observe’.‘Observe what?’ was their understandable reaction. Evenifthestudentshadsimplystartedtowritedownwhateverobservations struck them – the pen in their hand, the sun outside the window, a table made of wood, a floor with tiles on it – these would hardly have constituted anything approaching the coherence of a scientific theory. They would, on the contrary, have been nothing more than a random collection of unconnected facts. According to Popper, this little demonstration illustrates the completely unrealistic nature of the positivist idea that the scientist starts off by simply making lots of observations. For Popper, the scientist starts with a theory and then makes observations. Indeed, it is precisely in order to test the theory that the observations are made at all. This being the case, only certain, relevant observations will do, and it is one of the functionsofatheorytoguidethescientistinmakingthoseobservationsthat arerelevanttoitstesting.
But the problem with the positivist theory of completely neutral observation goes even deeper than this. It is, argues Popper, not only
impossibletomakecoherentandrelevantobservationswithouttheconcepts and expectations contained in a guiding theory, it is impossible to make any observations at all without such pre-existing knowledge. Even the student who, as in the above example, makes random observations of the pen, the table, the sun etc. can only do so on the basis of concepts that she already possesses. To perceive something as a table or the sun and to classify it as such requires pre-existing knowledge – one must already have the concept of ‘table’ in order to be able to class one of one’s current observations as being an exemplar of this particular category. For Popper, then, even our everyday, non-scientific observations require a theory (albeit perhaps an implicit one). Some of this knowledge is learned but, in addition, according to Popper, “we are born with expectations; with ‘knowledge’ which . . . is . . . prior to all observational experience” (Conjectures and Refutations, p. 47). It is here that the Kantian idea of the mind’s structuring of perceptionismostevidentinPopper’sthought.
Theirrelevanceofverification
The logical positivists argued that what differentiated real science from mere pseudo-science or metaphysics was that science could be verified through empirical observations whereas metaphysics and pseudo-science could not. This problem of differentiating between science and non-science was called the ‘problem of demarcation’ by Popper, and he pointed out that the logical positivists’ answer to the problem, verification, did not successfully differentiate science from non-science. Astrologists, said Popper, can point to lots of supposedly verifying facts that support their claims – every stubborn Taurean counts as a verification – yet astrology is notascience.Verification,therefore,cannotbethemarkofascience.
Popper’s misgivings about the importance of verification were further exacerbated when he considered the difference between Einstein’s theory of relativity and other supposedly scientific theories, such as Marxism, Freudian psychoanalysis, and the individual psychology of Adler. The followers of these theories, said Popper, could produce large amounts of data that appeared to verify the theories. Indeed such was the explanatory power of these theories that they seemed able to provide an explanation of just about any occurrence that one could think of. A naïve, verificationist
view of science would be impressed by a theory that can explain almost anything and has an enormous amount of empirical observations to verify it,butPopperwasnotsosure:
It was precisely this fact – that they always fitted, that they were always confirmed – which in the eyes of their admirers constituted the strongest argument in favour of these theories. It began to dawn on me thatthisapparentstrengthwasinfacttheirweakness.
(Conjectures and Refutations,p.35)
Einstein’s theory, however, was a different matter. One aspect of it was a gravitational theory that predicted that light would be attracted to heavy bodies in the same way that material objects were. This would mean that lightfromastarthatpassedneartotheSunshouldbedistortedbytheSun’s gravitational field. As the light from such stars is not normally visible, becauseitisoutshonebytheSun’sownlight,theonlywaythetheorycould be tested is during a solar eclipse, when the Sun’s own light is masked by the passing of the moon. This is exactly what was done by the astrophysicist Sir Arthur Eddington in 1919, who led an expedition to the island of Principe, off the west coast of Africa, in order to observe the starlight during a total eclipse of the Sun. Eddington’s observations confirmed Einstein’s predictions and became front-page news around the world.ThesewerethefirstempiricaltestsofEinstein’stheory.
ButitwasnotsimplytheconfirmationofEinstein’stheorythatimpressed Popper, it was what he saw as the risk involved in testing such predictions: there was a real possibility that the prediction might be wrong, and this would spell disaster for the theory that provided the prediction. “If observation shows that the predicted effect is definitely absent,” said Popper, “then the theory is simply refuted. The theory is incompatible with certain possible results of observation . . .” (Conjectures and Refutations, p.36).
In contrast, then, to the theories of Marx and Freud, for example, Einstein’s theory was distinguished by the fact that not all possible observations would fit with it. There were certain facts that could refute it. This, for Popper, was the strength of Einstein’s theory, and this is what he argued should be regarded as the criterion of demarcation between science
