A Study On Conceivability Thesis And Moderate Modal Skepticism

The thought experiment method is wildly used to prove philosophical conclusions.Many thought experiments are made of modal arguments,and those arguments are often based on modal statements of the form ‘it is possible that S’,in which S is of unknown truth value.Conceivability thesis is an important principle in modal epistemology which claims that there are special relations between a proposition’s conceivability and its possibility.Some researchers,such as Chalmers,assert typical conceivability must lead to possibility,while other researchers,such as Yablo,take conceivability as a fallible proof of possibility.Peter van Inwagen raised the theory of moderate modal skepticism in 1998 to question the popular thought experiment method and modal arguments behind it.According to van Inwagen,the soundness of modal arguments relies on modal statements,but many modal statements are not trustworthy because their truth value are unknown.It is unacceptable to construct arguments on such premises,let alone its conclusion.Moderate modal skepticism chooses conceivability thesis as the standard to judge truth value of a statement.Van Inwagen distinguishes modal statements into two parts,basic modal statements and non-basic ones invoking Yablo-style conceivability thesis.After that,his followers develops moderate modal skepticism,and clarifies the problem it tries to solve.This thesis is to show that moderate modal skepticism indeed shows the crux of the problem thought experiments face,which is mismatch of possibilities of different levels,by finding the dilemma of conceivability thesis.It may lead to a new way of understanding and solving the problem if researchers become aware of the levels of possibilities.On the frame of this thesis,first,it clarifies notions relating to conceivability thesis and emphasizes two conceivability theories put forward by Chalmers and Yablo.Chalmers’ s theory requires an omniscient subject,while Yablo’s theory count conceivability as fallible proof to possibility.Second,I shall analyze moderate modal skepticism and its improvements.As the forerunner,van Inwagen points out the importance to stay skeptic on non-basic modal statements.Hawke gives a formal version of van Inwagen’s argument.Feng’s examination supports moderate modal skepticism under two-dimensional semantics.Their works,in together,show that moderate modal skepticism is persuasive in explaining the dilemma conceivability thesis faces and in proving abuse of non-basic modal statements in thought experiments.Last,I shall show that moderate modal skepticism is an attempt to revise abuse of logical possibility.Conceivability implies possibility,but the possibility is at least metaphysical,not logical.Modal arguments mismatched logical and metaphysical possibilities.This thesis aims to achieve following goals: clarify the dilemma conceivability thesis faces by analyzing different forms of it;show the relation between moderate modal skepticism and conceivability thesis;pointing out that modal skepticism is based on the dilemma;analyze the theory of moderate modal skepticism,distinct its domain,and provide a philosophical interpretation for moderate modal skepticism with the hierarchy of possibility.