William Seager

Our knowledge forms a highly interconnected and dynamically changing body of propositions. One obviously important way that knowledge changes is via rational inference, based either upon new insight into the content of what we already know or upon new knowledge provided by the senses. The most obvious codification of the acceptability of inference driven knowledge growth is the so-called known entailment closure principle, the principle that if S knows that p and knows that p implies q then S knows that q, or, more formally.

Donald Davidson espouses two fundamental theses about the individuation of mental events. The thesis of causal individuation asserts that sameness of cause and effect is sufficient and necessary for event identity. The thesis of content individuation gives only a sufficient condition for difference of mental events: if e and f have different contents then they are different mental events. I argue that given these theses, psychological externalism--the view that mental content is determined by factors external to the subject of the relevant mental events--entails that the token identity theory is false