Natural Deduction

Abstract

In the previous chapter, we have been concerned with truth values of propositions, and also with relationships between propositional forms, namely equivalence and semantic entailment, which can be defined in terms of truth values. In this chapter we shall be looking at how we can argue from a given set of propositions known as premisses to obtain a further proposition known as the conclusion. There are many such ways in which we can justify an argument, not all of which are acceptable in logic. Consider the following example.