Rationality, utility and deontic reasoning

In this chapter, we are interested in one extremely important type of deontic reasoning, which takes place when people try to find out which actions they ought to perform or may perform. This type of reasoning has traditionally, in philosophy, been called ‘practical reasoning’ and distinguished from ‘theoretical reasoning’, which has the object of trying to discover, or to describe correctly, objective matters of fact. It is sometimes said that the difference between these two is that between trying to infer what one should (or may) do as opposed to trying to infer what one should (or may) believe. The latter does not have to be ‘theoretical’ in the scientific sense, and could be directed towards ordinary facts which are highly relevant to practical questions about what one should or should not do, for example, facts about what is healthy or unhealthy. Practical reasoning depends, in part, on some degree of theoretical reasoning, but goes beyond it to conclusions about actions. As with so much in the study of reasoning, Aristotle was the first to discuss practical reasoning systematically, and yet we still face many difficulties in specifying generally what it is for this reasoning to be rational, though we can often recognize that it has this property in particular cases. (See Audi, 1989 , on practical reasoning and the history of its study.)