PREFACE

Preface “Let ‘q’ be an arbitrary sentence of the language and suppose that the theory is inconsistent. This means that we can derive the sentence ‘p and not-p’. From this ‘p’ follows. And from ‘p’ it follows that ‘p or q’ (if ‘p’ is true then ‘p or q’ will be true no matter whether ‘q’ is true or not). Equally, it follows from ‘p and not-p’ that ‘not-p’. But ‘not-p’ together with ‘p or q’ entails ‘q’.”