Logic ought to guide our thinking. It is better, more rational, more intelligent to think logically than to think illogically. Illogical thought leads to bad judgment and error. In any case, if logic had no role to play as a guide to thought, why should we bother with it?

The somewhat naive opinions of the previous paragraph are subject to attack from many sides. It may be objected that an activity does not count as thinking at all unless it is at least minimally logical, so logic is constitutive of thought rather than a guide to it. Or it may be objected that whereas logic describes a system of timeless relations between propositions, thinking is a dynamic process involving revisions, and so could not use a merely static guide. Or again the objection may be that there is no such thing as logic, only a whole variety of different logics, not all of which could possibly be good guides.

I aim to disarm the last two objections to the initial idea that logic should be a guide to thought.

Logic and belief revision

How could logic guide our thought? Anything we can believe has an infinite number of logical consequences, but no sensible guide would tell us to take steps to believe all the logical consequences of anything we believe, for there is not enough time to obey and most of the added beliefs would be trivial.

There is something to the idea that we should consider our beliefs not just one by one but in larger groups, to see if we can logically extract some useful further information.