Studies On Substitution Of Co-referential Names Based On Predicative View

According to the Principle of Substitutivity(PS),co-referential names can be freely substitutable without change of truth value in sentences.However,the principle was questioned and challenged by Frege and Saul.Frege found that the principle is invalid in intensional contexts,hence ‘intensional puzzle';he maintained that intensional contexts are standardly blamed for substitution failure.But Saul challenged this view and pointed that substitution failures can occur in extensional contexts as well.With respect to substitution failure in intensional contexts,some scholars modified PS by transforming the classic propositional logic into epistemic logic.In the author's opinion,the modification is not proper.It is because a sentence in the intensional context can receive two readings: de re reading and de dicto reading.On a de re reading,PS is valid while on a de dicto reading PS is not.And with respect to substitution phenomena in extensional contexts,previous studies mainly centered on three questions which should be answered all together.First,do anti-substitution phenomena occur in the extensional context,or is it a semantic illusion? Second,do co-referential names co-refer in those anti-substitution sentences? Third,do our anti-substitution intuitions go wrong? Furthermore,with regard to the substitution phenomena in both two contexts,can they be equated to analyze?Two viewpoints are put forward in response to the issues above.First,in extensional contexts occur substitution failures.It is not a semantic illusion;anti-substitution intuitions are correct,but co-referential names always co-refer in those sentences.Second,the substitution phenomena in both two contexts can be equated to analyze.This thesis,based on Fara's Predicativism,analyzes substitution phenomena in both intensional and extensional contexts from the perspective of possible-world semantics and by using related theories and methods,and provides corresponding proofs for viewpoints above.Accordingly,this thesis proposes a modified principle of substitutivity.