This essay develops the relation, implicit in Essay 11, of intentional action to behaviour described in purely physical terms; Davidson repeats from Essay 3 that an action counts as intentional if the agent caused it, and asks to which degree a study of action thus conceived permits being scientific. Davidson stresses the central importance of a normative concept of rationality in attributing reasons to agents ; because this concept has no echo in physical theory, any explanatory schema governed by the (...) concept is irreducible to physical theory. Davidson adduces several facts that prevent us from giving strict laws connecting reasons and action: first, we cannot give conditions that are not only necessary but also sufficient for an action to be intentional, using only the concepts of belief, desire, and cause----for we cannot specify the ”right way’ in which beliefs and desires cause actions ; second, a certain holism of the mental pervades explanations of human behaviour: we cannot assign beliefs and desires independently of and prior to the actions they cause, a point Davidson takes Ramsey’s work on subjective probability to have shown. Davidson appends a set of replies to critics, which clarify his attitude to psychology as a science, his analysis of statements of law, the principle of causal interaction, and the relation between mutually irreducible explanatory schema. (shrink)