Abstract

AB S TRACXof thesis entitled 'Wittgenstein and the Justification of Deduction' submitted by CHAN Ho Mun for the Degree of Master of Philosophy at the University of Hong Kong in April 1987 The central philosophical problem of this thesis is the justification of deduction. It is argued that the problem is closely related to the nature of rule-following, meaning and understanding, the discussion of which figures prominently in the writings of Ludwig Wittgenstein. The aim is to approach the problem through the writings of Wittgenstein. The present work can also be regarded as an exposition of his ideas on meaning, rules and understanding. It can be shown that Wittgenstein's early solution to the problem is a semantical one. The central thesis of this solution is: the validity of logical inference is justified by the senses of the propositions involved. This leads him to think that an account of the nature of logic requires a theory of sense which serves to explain logical relations between propositions. The appreciation of this line of thought is very crucial for the understanding of Wittgenstein's early work, for it is indeed the historical and theoretical entry point into his early philosophy. It was admitted by Wittgenstein himself that his early philosophy is the best alternative to his later philosophy, and indeed his early solution to the problem is a very good one. However, Wittgenstein came to think, with very good reasons, that it was wrong. His objection to the early solution deserves a detailed examination, and I attempt to provide one here. In his so-called 'transitional period', Wittgenstein begins to reject his early theory of sense, and finally the whole semantical approach is repudiated. This volte face stems from his diagnosis of misconceptions about meaning, rules and understanding, some of which are present in his early work. Yet this does not mean that Wittgenstein has another solution to the problem of deduction. Based on his later ideas on meaning, rules and understanding, and his later philosophy of logic, it can be shown that deduction needs no justification and that the sceptical doubt about the possibility of justification is misplaced. In other words, Wittgenstein does not answer the problem, but shows how it may be eliminated. ii.