Informal Logic

Abstract

Logic is the framework upon which rigorous proofs are built. Without some basic logical concepts, which we will study in this chapter, it would not be possible to structure proofs properly. It will suffice for our purposes to approach these logical concepts informally (and briefly). Though logic is the foundation of mathematical reasoning, it is important not to overemphasize the use of formal logic in mathematics. Outside of the field of mathematical logic, proofs in mathematics almost never involve formal logic, nor do they generally involve logical symbols (although we will need such symbols in the present chapter).

Logic is the hygiene the mathematician practices to keep his ideas healthy and strong.

Herman Weyl (1885–1955)