As readers of this blog know, I am not a big fan of the compartmentalization of knowledge, and specifically of a compertmentalization on which theological knowlege does not affect one's philosophical beliefs. Here I just want to note one thing. A lot of contemporary metaphysical arguments have some form rather like this:
Here's a phenomenon F. Look, it's puzzling. Here are three accounts of F. Look, they all fail. Here's a fourth account of F. Look, it doesn't fail for the reasons for which the three fail.We're then supposed to accept the fourth account.
But of course such arguments are weak (there is nothing wrong with weak arguments, except that strong ones are preferable). Unless there is a further argument that any account must be one of the four, while such argument provides evidence for the fourth account, it should not give one very strong confidence in the fourth account. And at least in such a case, if the theology has a rational basis (e.g., in apologetic arguments), it seems clearly unproblematic to say, e.g., "Ah, but the fourth account fails, too, because it contradicts transubstantiation."
After all, if the fourth account of F contradicts transubstantiation, then the philosopher who accepts the fourth account and accepts transubstantiation needs to revise her beliefs. She could do so by rejecting transubstantiation. But assuming there is the kind of rational basis for her acceptance of transubstantiation that we might expect an intelligent Catholic to have (e.g., she is appropriately convinced by the apologetic arguments that show that Christ founded a Church whose basic beliefs would always be true and by the historical evidence that transubstantiation was, at least at one point in history, one of the basic beliefs of the Church), wouldn't it be silly for her to reject transubstantiation merely on the grounds of the fact that we have not yet found a satisfactory account of F that coheres with transubstantiation, but we have so far found an otherwise satisfactory account of F that does not cohere with transubstantiation? The confidence engendered by arguments of the form that was given for the fourth account of F is just too low to make it rational to reject transubstantiation.
Consider, too, that the revision to her web of beliefs in rejecting the fourth account of F is likely to be much smaller than the revision in rejecting transubstantiation if she is Catholic. (If she rejects transubstantiation, she will need to reject conciliar infallibility or else go Orthodox and deny that Trent was an ecumenical council. In either case, a lot of other beliefs would likely have to change.) It would be strange indeed if such significant transformation of one's belief system were to be made rational merely by the fact that three accounts of F are unsatisfactory and the only one we know of that doesn't fail in this way contradicts transubstantiation.
What is further typically true of these kinds of metaphysical arguments is that the fourth account, while not subject to the deficiencies of the first three, has some implausible consequences, too, which the author finesses. Even if in fact the author of the argument is right that these implausible consequences are less problematic than those of the first three accounts of F, it seems really clear that at least in such a case bringing in the theological consequences is entirely appropriate.
(I sometimes argue for a significantly weaker conclusion than the one I hold. This is certainly true in this post.)