- In the philosophy of science, identity over time emerges as a central concern both as an ontological category in the interpretation of physical theories, and as an epistemological problem concerning the conditions of possibility of knowledge.
- In Reichenbach and subsequent writers on the problem of indistinguishable quantum particles we see the return of a contrast between Leibniz and Aquinas on the subject of individuation1.
- The possibility of rejecting the principle of the identity of indiscernibles2 has certain logical difficulties, leading us inexorably from ontology into epistemology. For the epistemological problem we attend to the differences that emerged between the (neo-)Kantian and logical empiricist traditions, also saliently displayed in Reichenbach’s writings.
- After examining the contrast between Kant's and Leibniz’s conceptions of empirical knowledge, specifically with respect to the irreducibility of spatiotemporal determinations, we explore an application of a neo-Kantian view to the same problem of indistinguishable quantum particles.
- Arguments and views concerning identity and individuation3 resurfaced in the twentieth century in philosophical discussion of quantum mechanics4 connected with discernibility.
- Much dealt mainly with the conditions of possibility of being, that is, the conditions under which named or described entities are identical or distinct.
- Beginning with Kant, however, traditional questions of metaphysics were transposed into a transcendental enquiry, that is, enquiry into the conditions of possibility of knowledge.
- Accordingly, we shall address this topic in two parts.
- I. CONDITIONS OF THE POSSIBILITY OF BEING: In general, the conditions under which something can be the case are not the same as those under which it can be known to be the case. It does not follow that something can be the case even if there are no possible conditions under which it can be known to be so. But the distinction suffices to allow us to start with the former. In doing so, we may engage in realist metaphysics - or, on the contrary, bring realism's limits to light.
- II. CONDITIONS OF THE POSSIBILITY OF KNOWLEDGE: Kant wrote that we precipitate ourselves 'into darkness and contradictions' by seemingly unobjectionable steps that 'transcend the limits of experience, [and so] are no longer subject to any empirical test'. The form of metaphysics he thus criticized can be avoided by turning instead to a transcendental enquiry, an enquiry into the conditions of the possibility of knowledge in a given subject area, with reference to both experience and understanding.
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