Abstract

To reject skepticism and lay the foundation for the certainty of knowledge, Kant raised the question of how synthetic a priori proposition is possible. In his solution, the new content of knowledge comes from the syntheses of experience a posteriori, and the universal necessity of knowledge is guaranteed by it’s a priority. Under the influence of Kant, the concept of a priori and necessity has long been regarded as coextensive. But Saul Kripke believes that this will confuse different philosophical fields: a priori is an epistemological concept, which involves the way or means of acquiring knowledge, and necessity is a metaphysical concept, which involves the possible ways or states of the world. The key point is that, on Kripke, there is no necessary connection between these two fields. He raised some famous examples of the necessary a posteriori. More remarkably, in his explanation of necessary a posteriori, although he did not clearly propose the distinction between epistemic possibility and metaphysical possibility, he had laid the foundation for this distinction. Furthermore, on Manuel Garcia-Carpintero and Josep Macia, when Kripke talks about necessary a posteriori by appealing to two relevant expressions, what he proposed can be taken as kind of ‘blueprint for 2-D accounts’. (Manuel Garcia-Carpintero and Josep Macia, 2006, p.2) There are different forms of two-dimensionalism in semantics. I will focus on David Chalmers’s epistemic version and Scott Soames’ criticism. With the framework of possible world semantics established by Kripke and others, David Chalmers’ epistemic two-dimensionalism deals with the relationship between epistemic and metaphysical modalities from a quite different perspective, and then gives an elegant definition to necessary a posteriori and other modal concepts. Scott Soames criticized two-dimensionalism based on Kripke's modal realism and essentialism, and developed Kripke's account of necessary a posteriori. But according to Chalmers, Soames also uses a two-dimensional system himself to analyze cases of the necessary a posteriori. In the first two part of this paper I will briefly introduce the epistemic two-dimensionalism and specify the similarities between Kripke-Soames and Chalmers when they interpret necessary a posteriori. In the third part I turn to their difference by the analysis of relationship between epistemic possibility and metaphysical possibility which is the key issue for illuminating necessary a posteriori.