The Fundamental Principle of Practical Reasoning

Abstract

The fundamental principle of practical reasoning (if there is such a thing) must be a rule which we ought to follow in all our practical reasoning, and which cannot lead to irrational decisions. It must be a rule that it is possible for us to follow directly - that is, without having to follow any other rule of practical reasoning in order to do so. And it must be a basic principle, in the sense that the explanation of why we rationally ought to follow this rule lies purely in the structure of our rational capacities themselves (and not, for example, in empirical evidence that we merely happen to have). This fundamental principle, it is argued, requires that you decide to do something only if the basis of your decision is such that (i) it is rational for you to believe that you have given the matter enough thought, and (ii) your actual deliberation does not warrant the conclusion that the chosen option is definitely worse than some other option that you have considered. A decision formed through reasoning is rational if and only if the agent followed this rule in making the decision. The claim that this is the fundamental principle of practical reasoning conflicts with Hobbesian approaches because it implies that practical reasoning aims not only at satisfying desires, but at forming beliefs about which options are better than others. It conflicts with Kantian approaches because it implies that to think of something as a good thing to do is not just to think of it as a rational thing to choose. This account also shows how to solve some famous controversies surrounding practical reason: the key is to understand how the rationality of concluding that one option is better than another is affected by our desires, our estimates of probabilities, and our moral judgments.