Summary | Aquinas's Argument for God

Formalizing Aquinas’s De Ente argument, we have:

1)     Whatever a thing has is either caused by its essence or some efficient external cause.

2)     Any being not identical with its act of existence is caused (implied by 1).

3)     No essence can cause a thing’s existence.

4)     Thus, everything not identical with its existence has some efficient external cause.  

5)     This chain of efficient external causes must terminate.

6)     There is a cause of all things whose act of existence is really distinct from its essence, whose act of existence is identical with its essence.

Some quick justification for each premise.

Premise 1 is Aquinas’s causal principle. I.e., if something cannot be explained by some internal principle (namely, a thing’s essence) then it must be explained by some external principle (namely, a cause). Seems reasonable enough, though one could claim (also reasonably) that this assumes PSR. I think this is right but unproblematic, because PSR is true.

Premise 2 simply follows.

Premise 3 assumes nothing can act unless it exists. Again, seems reasonable enough. Thus, no essence can cause its own existence, since it would already have to exist for it to do anything, including act as cause.

Premise 4 follows from exhaustive coverage. If something is not identical to its act of existence and if that something’s essence cannot cause its existence, then its existence has some efficient external cause.

Premise 5 is the usual regress problem. The quickest motivation here is just to say, “Look, if none of these things carry existence inherently, then they remain forever iffy (‘conditional’) unless and until we trace back or twist up to something that just is its act of existence.”

In other words, given that things exist, there must be a sufficient condition for being. However, if there were only things with a real distinction between there essence and existence (no matter how many and no matter how they’re arranged), there would not be a sufficient condition for being. Ergo, there must be at least one thing whose essence is identical to its act of existence that stands as Primary Cause. “And that every knows to be God.”

Of course, this phase of argumentation assumes we have already established beings wherein there is a real distinction between their essence and existence.

More to come. But in the meantime, see: