A new perspective on rationality The foundations of decision theory and game theory are commonly thought to be settled, yet there are many examples of human behaviour which is not rational in the way these theories describe. We spoke to Professor Wolfgang Spohn about his work in re-examining basic normative questions about rationality, which could shift the normative reference point for empirical research. Our model of rational human behaviour has been fundamentally shaped by the development of modern decision theory and game theory. “The basics of these theories are thought to be somehow settled for decades – erroneously,” says Wolfgang Spohn, Professor of Philosophy and the Philosophy of Science at the University of Konstanz. The point is not that these theories are often conflated with the model of homo economicus, which assumes that we are primarily guided by rational self-interest and prioritise our own economic concerns. Such assumptions about specific individual values do not belong to the basic conception of rationality. Still, there are many examples of human behaviour which seem rational, but are not regarded as such by standard decision and game theory. While most research
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tinkers round the edges of existing theory, Professor Spohn aims to re-examine the foundations of rationality in a new Reinhart Koselleck project. “The basic normative questions about rationality are not settled. They are still contentious, and I want to take them in a specific direction,” he says.
Normative theory of rationality Professor Spohn’s inquiry into the foundations of a normative theory of rationality could fundamentally change the reference point for all empirical research. “Empirical research proceeds from the standard normative picture and then tries to find explanations for how and why we deviate. But if that standard reference point is not the correct one, then the focus of empirical research should shift,” he explains.
In traditional decision theory and game theory, formal structures called trees are used to represent different options of the agent and the various ways in which a situation may develop. “Two kinds of nodes are usually distinguished in a tree, the action nodes and the chance - or nature’s - nodes. I want to add a third kind of node, which I call decision nodes,” outlines Professor Spohn. “These decision nodes represent not the options of the agent, but rather the decision situations themselves that she is in, or may get into. They represent possible mental states in which she takes a decision and chooses an action.” The label ‘reflexive’ in the project’s title precisely refers to the reflection on those mental states. The decision nodes as described are something that Professor Spohn believes should be additionally represented within
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theoretical frameworks, leading to a more general theory of rationality capable of dealing with a wider range of situations. For instance, while standard theories only deal with the ways your decision situation may improve through the addition of more information, the more general theory can also deal with questions such as: How do you rationally behave today, when you expect to have forgotten something important tomorrow? How do you rationally take into account the fact that your preferences may be different tomorrow?
expressions for example. They therefore have an influence, particularly on social environments which are receptive to such influence. Again, the decision relevance of this aspect can only be captured in the reflexive perspective. This point is best exemplified in applications to game-like social situations. Such situations involve several ‘players’, and the outcome depends on their behaviour. They may be opponents or partners, or be entangled in some other way. The prisoners’ dilemma is a famous example, because it is a very common social situation.
The basic normative questions about rationality are not settled. They are still contentious, and I want to take them in a specific direction. Such questions call for a reflexive decision theory, modelling your reflection on your possible decision situations. Economists currently have only restricted models of preference change, an issue Professor Spohn is working to address. Another important aspect is the fact that decision-relevant mental states not only lead to rational action but are also expressed in other ways, through speech, emotions and facial
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In the original scenario, two criminals are arrested, but the police don’t have sufficient evidence to convict them on the more serious of two charges, so need a confession from one or both. If neither of them confesses, they can only be tried for a minor crime. If both confess, they will be imprisoned for a long time. However, if only one confesses, he is set free as the chief witness, while the other, showing no repentance, is even more severely punished. “Thus, both
rationally confess. At least this is what all game theorists say,” says Professor Spohn. The same social structure (reduced to two persons) is exemplified with the decision to get vaccinated in the table below. Both are better off when getting both vaccinated than both getting not vaccinated. But each is still better off when only the other one gets vaccinated. If so, both seem rational in not getting vaccinated. In the original example, the two prisoners can’t communicate. They don’t see what the other does, so their actions are causally independent. “Standard game theory concludes from this that the two decisions are also probabilistically independent. However, that’s a mistake,” claims Professor Spohn. The prisoners may have collaborated over the years and thus have developed an awareness of each other’s mentality, a kind of causally entangled, joint mental setup. This causal entanglement creates a common cause structure of their actions (confessing or not confessing), thus rendering them probabilistically dependent, even though they are causally independent. Just as fever and cough are correlated, but do not cause each other; rather, both are caused by an infection. “The standard solution concept of game
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