Six decades ago, when most men smoked, British doctors linked smoking to lung cancer, making it the first disease to be causally linked to smoking.

He is probably best known for his controversial modal realist stance that (i) possible worlds exist, (ii) every possible world is a concrete entity, (iii) any possible world is causally and spatiotemporally isolated from any other possible world, and (iv) our world is among the possible worlds.

argued that this was not a tenable theory, and that in fact whom or what a person's beliefs were about was in large part (or entirely) a matter of how they had acquired those beliefs, and those names, and how if at all the use of those names could be traced causally from their original referents to the current speaker.