Ed, I am going to take the liberty of first replying to your response to my answer to your fourth question. I am going to do this because I think that this is where we most significantly clash, that is, where our fundamental disagreements are most apparent. I want to address these points right away, and the others I will take up after the 15th when I will be back at my office.

Sorry if I was unclear and gave a misleading impression. I do, in fact, think that the laws of nature are best conceived in terms of the powers and liabilities of the entities and systems of entities that make up the natural world. That is, natural regularities are ultimately explicable in terms of the dispositional properties—the powers and the liabilities—of physical things. The most fundamental laws are the active and passive potentialities of the most fundamental physical things—whatever those are. If and when science reaches explanatory “rock bottom,” it will be in terms of some set of simple entities, i.e. some set of entities which, since they have no constituents, will be nothing other than a set of irreducible properties in virtue of which those entities possess their capacities to act or be acted upon. Along with Harré, Madden, Bhaskar, and Cartwright, I “…take the Laws of Nature to be about the powers, dispositions, or tendencies of natural systems to bring about observable phenomena (Harré, ‘Laws of Nature,’ A Companion to the Philosophy of Science, ed. by W.H. Newton-Smith, p. 218).”

In short, I think you and I agree that explanatory hierarchies will come to an end (if they do come to an end) with an uncaused cause—something that has no causal antecedents and is the original, fundamental, or primordial reality that possesses a set of distinctive properties which constitute the ultimate terms of every explanatory regress. I see no reason why that ultimate reality cannot be the original, fundamental, or primordial—and brutally factual—physical reality. Where is the incoherence? A brute fact would be a state of affairs that just is, with no cause or explanation of its existence or nature. There seems to be nothing about the idea of a brute fact per se that entails a logical contradiction.

You argue—quite correctly—that just because something is conceivable does not mean that it is realizable. You can conceive of impossible objects, and even illustrate them as in M.C. Escher drawings, but that does not mean that such objects are realizable in three-dimensional reality. But where is the incoherence or impossibility of the realization of a brute fact? What, if not logical inconsistency, would make brute facts unrealizable? Your answer is that a version of the PSR must be true. I quote your argument at length:

“Consider that whenever we accept a claim as rationally justified, we suppose not only that we have a reason for accepting it (in the sense of a rational justification), but also that our having this reason is the reason why we accept it (in the sense of being the cause or explanation of our accepting it). We suppose that our cognitive faculties track truth and standards of rational argumentation, and that it is because they do that we believe the things we do. But if PSR is false, then we can have no justification for supposing that any of this is really the case. We may in fact believe what we do for no reason whatsoever, and yet it might also falsely seem, again for no reason whatsoever, that we believe things for reasons. And our cognitive faculties may have the deliverances they do for no reason whatsoever — rather than because they track objective truth and standards of logic — and yet it might also falsely seem, for no reason whatsoever, that they do track the latter.

In short, either everything has an explanation or we can have no justification for thinking that anything does. No purported middle ground position, on which some things have genuine explanations while others are “brute facts,” can coherently be made out. If there really could be unintelligible “brute facts,” then even the things we think are not brute facts may in fact be brute facts, and the fact that it falsely seems otherwise to us may itself be yet another brute fact. We could have no reason to believe anything. Rejecting PSR entails the most radical skepticism — including skepticism about any reasoning that could make this skepticism itself intelligible. Again, the view simply cannot coherently be made out.”

For you brute facts are like Descartes’s evil genius. If we admit to such a possibility, it could show up anywhere, making us think that we have knowledge when we are really dead wrong. My first response will be a tu quoque: Affirming the PSR provides no protection at all against universal skepticism. It is one thing to think that things have sufficient reasons; it is something else entirely to say that we are in the epistemological position to discover them. We might go wrong every time we think that we have found the sufficient reason for anything. In Med. III Descartes famously attempted—using nothing but his own ideas and the PSR (or a principle very close to it)—to prove that a good God exists who will not allow us to be constantly deceived. By nearly universal philosophical consent, Descartes’s argument failed. So, to anyone who tries to succeed where Descartes failed—i.e. to prove the existence of a good God using only his own ideas and the PSR—I will only say “Lotsa luck!” It seems, then, that once the boogeyman of universal skepticism is set loose, merely affirming the PSR will not put him back in his cage again. Indeed, the very reasons we adduce for accepting the PSR could themselves be wrong (as, I maintain, they in fact are!).

But is it really so that “…either everything has an explanation or we can have no justification for thinking that anything does?” Why do we think that some things have explanations? Not for any a priori reason but just because we find that they do. Ancient astronomers discovered that the explanation of lunar eclipses is that the moon moves into the earth’s shadow. Finding that the moon sometimes moves into the earth’s shadow is simply the discovery of a fact about the world—a fact that explains another fact. When you stop and think about it, the early Pre-Socratic philosophers really went out on a limb to think that you could explain natural things in terms of other natural things. They had no a priori guarantee of success, and prior accounts had invoked gods and magic. Yet no Las Vegas jackpot has paid off as lavishly as that speculative leap. Success breeds confidence, and finding scientific explanations is the biggest success story the human race has to tell.

Could we be wrong about everything? Sure, if by “could” we mean “is a logical possibility”—and, again, the evil genius is not exorcised merely by invoking the PSR. But—and this is the only answer to the bogey of universal skepticism—the logical possibility that I could be wrong is insufficient reason to think that I might actually be wrong. All contemporary epistemologists of whom I am aware are fallibilists, that is, they hold that we can know that P even if possibly not-P. For skepticism to have any bite against a fallibilist epistemology, it must do more than simply indicate that we could be wrong. The skeptic must take on a burden of proof and show not just that mistakes are possible but that they have some significant degree of probability. Likewise, for your skeptical argument to be cogent, you would have to show that your scenario is not only possible but significantly probable. That is, you would have to show that, given the possibility of brute facts, they are likely to pop up even where they most clearly seem to be absent, i.e. where we seem most clearly to have reliable explanations (e.g. lunar eclipses).

Finally, what about the terms used to justify the claims that God is self-explanatory? Did I unfairly dismiss these as ad hoc devices? The fact that a concept has a respectable pedigree does not mean that it has legitimate application in a given context. As you note, the actuality/potentiality was developed by Aristotle to deal with the challenge of the Eleatics about change. There is nothing wrong with concepts of actuality and potentiality per se; indeed, as I indicate above, I endorse their use in the philosophy of science. But, as Kant argued at great length, even concepts that are quite innocent in one environment can become obscurantist in another. Such—or so it appears to me—is the case when the innocent actuality/potentiality distinction becomes the basis for saying things like “God is pure actuality” or “God is the act of existence.” It makes sense to say that something actualizes its potential, but even if something actualizes all of its potentials, it does not thereby become “pure actuality”—whatever that is. We speak meaningfully of tasks being completed but nothing is “pure completeness.” An empty vessel can be filled, but nothing is “pure fullness.” “Actuality,” like “completeness” or “fullness,” seems to me to be an abstract noun that has it uses but cannot constitute the identity of a substance.

BTW, saying, as I did, that these terms sounded obscure and fishy to me was a personal confession, not a blanket condemnation. The EPR paradox sounded obscure to me until Prof. John Earman explained it to me in grad school. Saying how these terms sound to me was not a dismissal but an invitation to be instructed. Tell you what: If you will send me a (signed, if you would) copy of your book Scholastic Metaphysics, I will read it carefully and give it a thorough review.

I will address your other responses after 3/15. Thanks much for this enjoyable and informative exchange.