I suspect this to be incoherent ...

Are you suspecting that David Braine's argument is incoherent, or are you suspecting the reason why what he calls incoherent is, in his view, incoherent?

Blaine's argument seems to me to rest on two ideas:

(1) Any direct consequence of a nature's activity must be contemporaneous with that activity. In other words, an action at time t₀ cannot "reach into the future" to have a direct effect at some later time t₁. Only actions at t₁ can have direct effects at time t₁. For, at time t₁, actions from earlier times no longer exist (on this view), so no such action can be the direct cause of anything at t₁.

(2) If a nature N "explains" the existence of a thing T, then it must be the case that, were T not there, but (roughly) all else were "as equal as it could be", then something would have to have been actively blocking N from bringing about the existence of T. That is, T's nonexistence (while all else is "as equal as it could be") must entail the existence of such a "blocker". Otherwise, N can't really be accounting for T's existence.

With that in the background, I'd interpret Blaine's argument to be as follows:

First, some premises. In conformity with idea (1) above, each premise is "tensed", in the sense that each proposition is to be taken as a description of the world at a particular time. For example, in each implication, the consequent is taken to be true when the antecedent is true.

Premise 1. A fact F can be explained by appealing to a nature N only if, at some time, a truthmaker of F "flowed" from N.

(I'll be putting "flow" in quotes because I don't want to define exactly what it means. The logical role played by the word should be clear from where it appears in the premises of the argument.)

Premise 2. Some truthmaker of a fact F "flows" from a nature N only if the following counterfactual implication is true:

(CI) Were every thing that actually exists just as it actually is, except that no truthmaker of F existed, then some thing would be blocking a "flow" from N (namely, that "flow" that is actually producing a truthmaker of F).

(Here, "just as it actually is" means that the thing's nature, in the counterfactual scenario, would be active in just the same way that it is in the actual world. Any difference in the nature's effects is due to a difference in the exogenous obstructions to that nature's "flow".)

Premise 3. Necessarily, if some thing is blocking a "flow" from a nature N, then that "flow" exists [albeit unable to accomplish what it would have were it not being blocked].

(Here, "necessarily" just means that we can deploy this premise even within counterfactual scenarios.)

Premise 4. Necessarily, if a "flow" from a nature N exists, then a thing with nature N exists.

Premise 5. It is a contingent fact that something with the nature of the stuff of the universe exists.

(That is, we can entertain counterfactual scenarios in which no such stuff exists without generating an ex contradictione quodlibet explosion of consequences.)

The argument then proceeds as follows. Let N be the nature of the stuff of the universe, and let F be the fact that something with this nature exists.

We first show that the counterfactual implication (CI) in premise 2 is false for this value of N and F. By premise 5, (CI) is not trivially true (i.e., true only because the antecedent is necessarily impossible). In particular, once we have shown that the antecedent of (CI) entails the negation of its consequent, we will have shown that (CI) itself is false. To that end, suppose that no truthmaker of F existed. Then no thing with nature N would exist. Thus, by the contrapositive of premise 4, there would be no "flow" from N. Hence, by the contrapositive of premise 3, no thing would be blocking a "flow" from N. Therefore, (CI) is false.

Now, by the contrapositive of premise 2, it follows that no truthmaker of F "flows" from N. Hence, by the contrapositive of premise 1, it follows that F cannot be explained by appealing to the nature of the stuff of the universe. This proves the claim.

Most of the work in this argument is being done by premise 2. That's probably the point at which a skeptic would accuse the argument of begging the question.

Last edited by Tyrrell McAllister (6/26/2017 9:24 am)