ABSTRACT
Philosophers have for many years made a broad distinction between two forms of reasoning: pure or theoretical reasoning on the one hand, and practical reasoning on the other. Pure reasoning is largely about matters of fact: It is the kind of thinking we are doing when we try to figure out what is the case, as when we consider whether a certain statement is true or not. For instance, suppose we assume that the following statement about students is true:
We learn that a certain student, Jasper, works hard. We conclude, validly, that he does well on tests. Practical reasoning, by contrast, is largely concerned with inferences about which actions may be performed or not. Suppose now that one accepts the following statement:
Note that now we are talking about accepting a statement, rather than assuming truth, and that the consequent contains a modal auxiliary verb, should, instead of the plain indicative construction in the first example. Such features mark out this second statement as one calling for practical reasoning. Now again we learn that Jasper works hard, and so we conclude that Jasper should rest on Sundays. This particular example illustrates a form of deontic reasoning involving a conditional obligation; other varieties have to do with permission, promise, and so forth.
