A counterfactual of the form ‘If it were the case that p, then it would be the case that q’ is said to be true if and only if, in the closest possible world in which p is the case, q is also the case – where the ‘closest’ possible world in question is the one in which p is the case but otherwise differs minimally from the actual world.Lowe followed that with what would, until relatively recently, have been a stunningly fallacious argument against mental physicalism, all wrapped up in PW talk: a gift to any intelligent physicalist, who’s thence able to refute an objection to her position that comes with all the modern trappings of the authority of modern philosophy. But to step back a bit, what’s wrong with Lewis’s analysis? To begin with, subjunctive talk equivocates like anything. And then there’s the problem of saying what is, in the relevant way, possible; a problem Lewis solved in an implausibly Humean way, which was at least elegant in a principled way, if evidently false. And of course, what is to count as ‘close’?
......Suppose I’m trying to tell you something, and I know (since I know what it is) that you’ll find it hard to understand what I’m saying. I might say, ‘If you knew what I was trying to tell you, you’d know how difficult this is.’ But of course, if you did know then it would be trivially easy to tell you about it. Perhaps I meant that after I’d told you, and you’ve understood me, you’d agree that it was difficult to tell you. But suppose it’s so hard to tell you that you never do get it. Does my meaning really depend upon which of the possible worlds in which I’ve told you is most like the actual world, in which you didn’t get it?
......What if the difference is just a few neurones that you were born with, for example, but that those neurones also make it hard for you understand why it was difficult to tell you (since you then find such things so obvious)? What if lots of things; and so basically, how could all that really affect the meaning—and hence the truth—of what I’m saying? After all, we do seem to have got bogged down in an awful lot of fallacious arguments and counter-argumetns since the 1970s; which may be ideal for professional philosophers in a stupid economy, but less so for those applying logic to the real world.