WHAT IS LOGIC?

nevertheless reasonable to identify logic as the study of inferences and inferential

relations. The obvious practical use of logic is in any case to help us to reason

well, to draw good inferences. And the typical form the theory of any part of logic

seems to be a set of rules of inference.

This answer already introduces some structure into a discussion of the nature of

logic, for in an inference we can distinguish the input called a premise or premises

from the output known as the conclusion. The transition from a premise or a

number of premises to the conclusion is governed by a rule of inference. If the

inference is in accordance with the appropriate rule, it is called valid. Rules of

inference are often thought of as the alpha and omega of logic. Conceiving of logic

as the study of inference is nevertheless only the first approximation to the title

question, in that it prompts more questions than it answers. It is not clear what

counts as an inference or what a theory of such inferences might look like. What

are the rules of inference based on? Where do we find them? The ultimate end

one tries to reach through a series of inferences is usually supposed to be a true

proposition. Frege [1970, 126] wrote that “the word ‘true’ characterizes logic.” But

how does this desideratum determine the rules of inference? A few distinctions

will illustrate the embarrassment of riches covered by the term “logic” and at the

same time sharpen the issues