Abstract

Logicians have long recognized a distinction between categorical, conditional and hypothetical reasoning. Roughly speaking, categorical reasoning exhibits the form "? since ?". Conditional reasoning exhibits the form "If ? then ?". Hypothetical reasoning exhibits the form ?Since ?, it is reasonable to suppose (conjecture, hypothesize) that ?¬. Categorical and hypothetical reasoning is a matter of drawing consequences. Conditional reasoning is a matter of spotting consequences, not drawing them. Categorical reasoning maps belief to belief. Conditional reasoning engenders implicational belief. Hypothetical reasoning maps belief to supposition (conjecture, hypothesis). Since the notion of belief is a constituent of reasoning in all these forms, it is only natural to suppose that it will have a role to play in the differentiation of good and bad reasoning. A logic of reasoning should have something to say about this. In the account developed her, belief has a central importance. In chapter two, I made favourable mention of the Can Do Principle. This is the principle that bids us, to the extent possible, to solve our theoretical problems in frameworks that are up and running and successful, using methods that are tried and true. I said that, provided it does not overreach itself, Can Do gives to the theorist methodological guidance of the first importance. For the better part of twenty-five years, belief-change theories have been a prominent part of the research programmes of AI[1] and formal epistemology.[2] If reasoning comprehends belief-change, why wouldn’t a theory of reasoning be an adaptation of a theory of belief-change? Wouldn’t a theory of belief-change be the natural place to look? Isn’t this what Can Do would suggest? Similarly, belief has been the focus of attention of modal logicians for nearly fifty years. Would a belief logic also be a natural place for a logic of reasoning to seek instruction? Wouldn’t Can Do also direct us here? This is not, in fact, the course that I am going to take..