TWO APPROACHES TO INSTRUMENTAL RATIONALITY

Suppose I intend end E, believe that a necessary means to E is M, and believe that M requires that I intend M. My attitudes concerning E and M engage a basic requirement of practical rationality, a requirement that, barring a change in my cited beliefs, I either intend M or give up intending E. Call this the Instrumental Rationality requirement – for short, the IR requirement.

Suppose now that I believe that E, and I also believe that E will only occur if M. My beliefs engage a basic demand of theoretical rationality, a demand that, roughly, either there be a change in at least one of these two beliefs or I believe M. Call this the Belief-Closure requirement – for short, the BC requirement. BC, note, is not a consistency demand on my beliefs: failure to add the further belief that M need not involve inconsistency in the way that adding a belief that not-M would. Nevertheless, something like BC seems a basic rationality constraint on belief.

Both IR and BC express constraints on the coherence of the agent's relevant attitudes; and these constraints are aspects of the normal rational functioning, in the psychic economy of believing-and-intending agents, of the cited attitudes. The intentions and beliefs of such agents will tend to be responsive to these constraints. But the requirements differ in important ways.