(P1) If there are moral facts, then their basis is either natural or supernatural (where these two are construed as mutually exclusive categories)
(P2) The basis of moral facts is not natural
(C1) Therefore if there are moral facts, then their basis is supernatural
(P3) The most plausible way to think of a supernatural basis of moral facts is in terms of a supernatural person who brings moral facts about.
(C2) Therefore, if there are moral facts, the most plausible way to think of their basis is in terms of a supernatural person who brings moral facts about.
Before I start in on my observations, I think it is important to point out that Dr. Peoples’ original blog post was just giving a reader’s digest version of the argument, so it would be uncharitable to act as if this is the final and definitive statement from Dr. Peoples on the subject. I’m sure if given the time and space, Dr. Peoples could give a very robust defense of the MAT.
My first comment concerns the first two premises and the first conclusion. (P1) is a conditional statement (if X then Y) that leads to a disjunction (either A or B). Dr. Peoples then uses (P2) to introduce the negation of one of the possible options, leaving us with (C1).
Dr. Peoples’ deduction of (C1) from (P1) and (P2) is of course valid, but I think it presents a false dilemma. Dr. Peoples’ states:
And since the natural and the non natural are mutually exclusive, that is, they cover all possible options, then there’s just no avoiding it: If there are any moral facts then their basis has to be either natural or supernatural.
(emphasis is mine)
I agree that natural and non-natural are mutually exclusive, but they are not jointly exhaustive (e.g. they cover all possible options) and I think Dr. Peoples engages in the equivocation of non-natural and supernatural. A distinction needs to be drawn here to escape this equivocation, supernatural is not merely the negation of the natural, and anything non-natural is not ipso facto supernatural. To bolster my case:
The more general application is to philosophy as a whole, and again involves both the objects studied and the methods used in studying them, I.e. both metaphysics and epistemology. In metaphysics naturalism is perhaps most obviously akin to materialism, but it does not have to be materialistic. What it insists on is that the world of nature should form a single sphere without incursions from outside by souls or spirits, divine or human, and without having to accommodate strange entities like non-natural values or substantive abstract universals (The Oxford Companion to Philosophy, Ed: Honderich, Oxford, 1995 page 604)
Notice this entry draws the same distinction I asserted earlier, that there can be non-natural entities like abstracta, that are clearly not natural and clearly not supernatural. If Platonic numbers exist, they are abstract and cannot causally interact with the concrete world, which I think is counter intuitive to the conception of the supernatural, since it is so often invoked as an explanation of phenomena.
So I would insist that Dr. Peoples’ (P1) add another disjunctive:
(P1’) If there are moral facts, then their basis is either natural or non-natural or supernatural (where these three are construed as mutually exclusive and jointly exhaustive categories)
And of course, if this change is made, (C1) does not follow from (P1’) and (P2) and the original force of the MAT fails to materialize.
A second observation that I think needs to be made is that I think Dr. Peoples might be close to error in his alethic modality. Take for example this section of his blog post:
Notice firstly that this more nuanced version of the moral argument doesn’t prove that God exists. What it establishes is that if there are moral facts, then they are best explained by a supernatural person who is the source of moral truth. But I think that the existence of a being like that is obviously not compatible with philosophical naturalism, the belief that the natural universe is all there is: Matter, energy and nothing else. So what we have is a contingent claim. If moral facts exist, then philosophical naturalism is false and there exists, for want of a better term, something like a God.
Notice secondly that this argument has a further logical consequence: If no supernatural person exists, then there are no moral facts. That is the real kicker here, and I think that’s why a number of atheists are, on an emotive rather than intellectual level, so strongly opposed to the moral argument for theism. The moral argument effectively says to them that they are denying that moral claims are true, and who wants to be in that position?
And to add to this, his closing remarks:
In short, whatever else might exist in a godless world – and that’s a subject for a whole other discussion – moral facts certainly could not exist.
(emphasis mine again)
I think it worth mentioning as a word of caution here, while it might be necessarily “that if Naturalism is true, then moral facts do not exist“, it does not follow to say “moral facts necessarily could not exist in a naturalistic universe”. The scope of modality expressed by Dr. Peoples is quite broad:
Notice secondly that this argument has a further logical consequence: If no supernatural person exists, then there are no moral facts.
What I gleaned from the blog post was:
Let N be “ If naturalist is true” and ~M be “moral facts exist”
(P4) Nec(N -> ~M)
(C3) N -> Nec(~M)
Which would qualify as a modal fallacy.
The broadest in scope and strongest type of necessity is that of logical necessity, which I think Dr. Peoples comes close, if not outright, stating is the case. I think perhaps it might be appropriate to take a softer stance then stating moral facts could not logically exist in any possible world without the supernatural is not something I think could be defended.
While the debate over the truth value of (P2) and (P3) is of much interest to me, I think Dr. Peoples’ MAT and presentation of MAT needs some tweaking, it raises some important questions that Atheist and Theist alike need to carefully examine.