Historically, many epistemologists have understood evidence/ reasons for belief as non-factive: a visual experience as of a red sock is good evidence that the sock is red, regardless of whether that experience is veridical or hallucinatory. On this picture, you and your mental-state duplicate who happens to be a brain in a vat are also epistemic duplicates.

Recent decades have witnessed a factive turn in epistemology: a turn towards conceiving of evidence/ reasons for belief as being importantly constrained by facts about your environment. On this way of thinking, you and your BIV duplicate are not epistemic duplicates: your environment really does include the cat on the mat, so perceptual experience as of the cat on the mat is accurate, and your belief that the cat on the mat is true. Your BIV duplicate’s environment does not include a cat on a mat, so its experiences are inaccurate/ beliefs are not true. As a result, claims the factivist, the BIV lacks evidence that you possess, and has less rational beliefs.

This semester we’ll examine three related manifestation of factive turn. First is Williamson’s knowledge- first programme, on which one’s evidence consists in all and only the propositions that one knows. Since knowledge is factive, those propositions must be true. The second is Dancy’s theory of reasons, no which only facts can serve as reasons for belief and action. The third manifestation is disjunc- tivism, of which there are two main types. Metaphysical disjunctivism is the thesis that facts about the environment can serve to individuate subjectively indistinguishable experiences, e.g. it might dis- tinguish between your cat-on-the-mat experiences and those of your duplicate. In contrast, Epistemic disjunctivists hold that you are in a better epistemic position than your BIV duplicate, but they needn’t make any claims about differences in your mental states. Clearly epistemic and metaphysical disjunctivism are natural allies, though they can come apart.