It’s no secret that Edward Feser is a big fan of Thomas Aquinas. One could even say that Feser is somewhat of a ‘popularizer’ of Aquinas. In particular, Feser specializes in Aquinas’s natural theology (i.e. arguments for God’s existence). Feser himself believes that Aquinas’ arguments are airtight arguments. Naturally, I would say that I am quite skeptical of any philosophical argument being airtight. I’m not saying that Feser is claiming that his arguments contain premises that are absolutely certain (in the Cartesian sense), but Feser himself has said that Aquinas’ arguments demonstrate that God exists with ‘metaphysical’ certainty.
One of the basic ideas in Aristotle and Aquinas’ metaphysics is the idea of material causality. Material causality doesn’t mean that the material cause is always material in the sense of being physical or natural. Hence, if we were to say every effect has a material cause, we are not presupposing the truth of naturalism, materialism, or physicalism. That’s one of my objections to, for example, Aquinas’s second way (and other cosmological arguments).
Aquinas’s second way says that every effect has a cause and that we see causes in nature. However, this is an incomplete description of what is actually happening. What is actually happening is that we see effects with material causes. It seems that every effect has a material cause. Or, at least, people like Feser (who thinks the argument is sound) have the burden of proof to demonstrate that this causal principle is more plausible that the principle of material causality. Feser has the burden of proof because he is the one running the argument. Not only is Feser committed to the claim that God created the beginning of the universe without any “material” cause, but Feser is also committed to the claim that God is upholding the universe every second without any material cause! It’s important to note that what I’m objecting to is not the same thing as the “interaction problem” of how a incorporeal soul could cause changes in the material world. Once again, that’s NOT my objection.
But what exactly is the principle of material causality (PMC)? The PMC claims that every effect has a material cause, and/or every originating/sustaining cause has a material cause.
Feser might reply that my objection begs the question; however, this would be both a strawman and a shifting of the burden of proof. For one, I am not claiming that my principle is true or that Feser and Aquinas’s principle is false. Secondly, Feser has the burden of proof to demonstrate that his principle is more plausible than the principle I have been discussing; otherwise, Aquinas’s second way (and other cosmological arguments) is undermined. Once again, Feser has the burden of proof because he is the one running the argument and making the claim. The skeptic-one who is in doubt about an argument/premise- does not have the burden of proof. Thus, if we are in doubt about whether the PMC is true/false, then that is tantamount to being in doubt about whether Aquinas’ cosmological argument is sound. Hence, it won’t be enough for Feser to try and simply undermine the PMC; he must refute it.
So what’s the implication of my objection? Well if everything has a material cause, then creatio ex nihilo is false. In addition, God can’t sustain the universe (out of nothing) either. With respect to Feser’s interpretation of Aquinas’ cosmological arguments, the same problem arises. So even though Aquinas’ cosmological arguments are “part-whole” cosmological arguments (according to Feser), we still have the problem of God sustaining an (or multiple) essentially ordered/hierarchical series out of nothing.
A Thomist wouldn’t want to bite the bullet and give up doctrines like creatio ex nihilo. Even if they did, my objection entails that is is very far from clear why God would be needed to make sense of things like efficient/material causation. In fact, for all we know, God couldn’t play a role.  
 None of this is to say that I believe that the PMC is true, nor is it to say that I think every effect has a cause (or that everything that begins to exist has a cause)
 I don’t think Feser has responded adequately to Humean and Kantian criticisms of Aquinas (especially Kant). Thus, I plan to make some posts about them.