Instrumental Reasoning

Abstract

Like all reasoning, practical reasoning is a process that takes a person from some of her existing mental states to a new mental state. Theoretical reasoning concludes in a belief; practical reasoning in an intention. This paper concentrates on instrumental reasoning, one species of practical reasoning. It argues that instrumental reasoning is correct if the content of the reasoning is a valid derivation, just as theoretical reasoning is correct if its content is a valid derivation. It also argues that neither theoretical nor practical reasoning gives a reason for its conclusion. If a piece of reasoning is correct, it concludes in a state — a belief or an intention — that is rationally required by the states it is derived from, but rationally requiring a conclusion is not the same as giving a reason for it.

This paper was written while I was a visiting fellow at the Swedish Collegium for Advanced Study in the Social Sciences. I am extremely grateful to the Collegium for its generous support and hospitality. In the long course of my work on this subject, I have learnt a great deal from discussions with, or in some cases just passing comments from, Jeremy Butterfield, Jonathan Dancy, Sven Danielsson, Stephen Darwall, Jane Heal, Tito Magri, Adam Morton, Jan Odelstad, Derek Parfit, Ingmar Persson, Christian Piller, John Skorupski and Howard Sobel.