I spent a fun few days over the break at the “NYU Causation Conference”:http://philosophy.fas.nyu.edu/object/philo.newsevents.lapietra.html held at La Pietra just outside Florence. I’m not sure how widely disseminated anything said there was meant to be, but I think it isn’t too much of a violation of netiquette to talk about one of the big issues that came up.

In many areas of philosophy there is a debate between those who think a certain kind of feature of the world is fundamental, and those who think it is reducible to, or a feature of, other features. Consider, for instance, the debate between Descartes and Ryle. Descartes thinks that minds are fundamental features of reality, things that can (at least to a great extent) vary freely of physical facts. Ryle denies that minds are fundamental. Though there is some scholarly dispute over what his positive view is, we can all agree that he denies Cartesian fundamentalism about the mental.

Ryle makes an argument against Cartesian fundamentalism that is used by many other anti-fundamentalists. (Indeed, this style of argument came up at the conference.) The argument is as follows.

# If fundamentalism is true, then certain kinds of situations where the fundamental facts vary widely from other facts are possible. (E.g. the situation Ryle makes much of is that many people around us have no mental states at all.)
# If these situations are possible, we need to have a reason to rule them out before we know they are not actual.
# We have no such reasons.
# But we do know that such situations are not actual. (E.g. we know, for example, that Einstein was a genius, and hence had a mental life.)
# So fundamentalism is false.

Now there is a lot that can be said against premise 2. The best thing to say, as Brad Skow said at the conference, is that any such principle seems to lead to scepticism. We think that brain-in-vat situations are possible. And any sense of ‘reason’ strong enough to make premise 3 true will probably imply we have no reason to believe such situations are not actual. So we don’t, after all, know anything. (There are several gratuitous appeals to closure principles in both the argument and my reply, but I assume readers can fill in the details appropriately.)

At the conference there was a lot of discussion about whether this line of reply to the anti-fundamentalist argument worked in general, or on particular occasions. I wanted to make here one point that no one made there, and which for all I know hasn’t been made in the literature.

Assume for reductio that this epistemological argument really raises a problem for the fundamentalist. Then it seems there is just as much of a problem for the anti-fundamentalist. That is, assume Ryle is true that we don’t have a reason to rule out the kind of wacky situations the Cartesian says are possible, i.e. situations where physical behaviour and mental properties are totally out of whack. The point I want to press is that saying these situations are impossible doesn’t obviously help.

Most philosophers, not all but most, say that at least some of the time in order to know that _p_, we need to rule out certain _impossible_ situations in which _p_ is false. For instance, to know that Fermat’s Last Theorem is true, we need to rule out the situations, every one of them impossible, in which it is false. The obvious conclusion is that the impossibility of a situation is no reason to conclude we need not have a positive reason in order to know that it does not obtain.

There is more to be said here, and I might try and follow this up later, but I think that there is a big problem here for arguments like Ryle’s. If we have epistemological standards high enough that knowledge requires ruling out outlandish possibilities, such as the possibility of various properties that are always correlated in the actual world (and in most salient counterfactual worlds) coming apart, then we should also say that knowledge requires ruling out salient _impossibilities_. And then the Rylean argument that we can’t rule out those situations will imply an absence of knowledge, whether Cartesian fundamentalism is true or not.

_Disclaimer_: I don’t for a minute believe in Cartesian fundamentalism, or in most other kinds of fundamentalism that are philosophically popular. I just don’t think we can prove much metaphysically by going via epistemology, hence this little rant.