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After this lecture you should understand what decision theory is, why we need something to anchor a shared understanding among us, as researchers, of the notions of belief and desire, why it is at least theoretically coherent to construe decision theory as providing this, and why construing decision theory in this way is difficult or impossible to combine with accepting the dual-process theory of instrumental action.

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The overall aim of the course: to discover why people act, individually and jointly.

To have any chance of achieving this, we need a synthesis of:

  • the kind of theoretical framework provided by philosophical thinking;

  • a body of evidence provided by experimental psychology; and

  • a formal model.

At this point, we have considered all three items.

This lecture was about the formal models. The best studied, most influential of these is decision theory.

Why do we need decision theory, and how does it fit with the philosophical and psychological theories considered so far?

One possibility is that decision theory provides an elucidation of the notions of belief and desire that we need to characterise goal-directed processes (Jeffrey, 1983); see What Are Preferences?.

But, as we saw in Dual Process Theory Opposes Decision Theory?, it is not straightforward to combine this idea with the dual-process theory of instrumental action.

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decision theory : I use ‘decision theory’ for the theory elaborated by Jeffrey (1983). Variants are variously called ‘expected utility theory’ (Hargreaves-Heap & Varoufakis, 2004), ‘revealed preference theory’ (Sen, 1973) and ‘the theory of rational choice’ (Sugden, 1991). As the differences between variants are not important for our purposes, the term can be used for any of core formal parts of the standard approaches based on Ramsey (1931) and Savage (1972).
dual-process theory of instrumental action : Instrumental action ‘is controlled by two dissociable processes: a goal-directed and an habitual process’ (Dickinson, 2016, p. 177). (See instrumental action.)
goal-directed process : A process which involves ‘a representation of the causal relationship between the action and outcome and a representation of the current incentive value, or utility, of the outcome’ and which influences an action ‘in a way that rationalizes the action as instrumental for attaining the goal’ (Dickinson, 2016, p. 177).


Dickinson, A. (2016). Instrumental conditioning revisited: Updating dual-process theory. In J. B. Trobalon & V. D. Chamizo (Eds.), Associative learning and cognition (Vol. 51, pp. 177–195). Edicions Universitat Barcelona.
Hargreaves-Heap, S., & Varoufakis, Y. (2004). Game theory: A critical introduction. London: Routledge. Retrieved from
Jeffrey, R. C. (1983). The logic of decision, second edition. Chicago: University of Chicago Press.
Ramsey, F. (1931). Truth and probability. In R. Braithwaite (Ed.), The foundations of mathematics and other logical essays. London: Routledge.
Savage, L. J. (1972). The foundations of statistics (2nd rev. ed). New York: Dover Publications.
Sen, A. (1973). Behaviour and the Concept of Preference. Economica, 40(159), 241–259.
Sugden, R. (1991). Rational Choice: A Survey of Contributions from Economics and Philosophy. The Economic Journal, 101(407), 751–785.