I think Feser‘s greatest success is in his arguments for a re-consideration of Aquinas’ Aristotelian metaphysical ideas, especially with regard to causation, but also with regard to an ontology of potency and action, and hylomorphic (form/matter) dualism.
My main criticism is that while Feser’s assumed role as Aquinas’ champion is usually a benefit to the reader, as Aquinas is presented in most sympathetic light, he is inclined to insist that all of Aquinas' ideas are equally meritorious. In some cases this leads him to present arguments which seem to go beyond what would have occurred to Thomas himself.
But, with plenty of references for further reading, Feser has given the reader a roadmap for further study to follow onto his fine introduction.
Below are somewhat scattershot notes and comments I made while reading the book. To briefly summarize my own views: I'm attracted to some of the metaphysical elements of Aquinas/Aristotle as they relate to causation and mind, and I'm even sympathetic to some of the cosmological arguments. On the other hand, I was unconvinced by significant parts of the Thomist package, including arguments by analogy for some of the divine attributes, God's nature as pure act and his separateness from matter, and the special nature of the human soul.
Ch. 1 Aquinas (intro.)
Ch. 2 Metaphysics
P.12 The interplay of potency and act in explaining change is something I’m attracted to. One part of Aquinas’ view I didn’t see any motivation for was the presumed asymmetry whereby act is prior to potency. He says potency cannot exist without act, but act can exist without potency. This anticipates Aquinas’ hierarchy from God as pure act down through to prime matter as pure potency. But I think it is simpler to view all of reality as composed of both potency and act. And if God is the ultimate being, he should be the source of all potentia as well as the power to actualize them.
P.21 I agree neo-Aristotelian causation has merit. There is a lot of good current work on a powers/dispositions ontology which is simpatico.
P.24 Essences are difficult, and seem at first to be outmoded by the essentially quantitative differences among physical objects. However, I’m open minded: perhaps if all the infinite possibilities are considered, there is a set of overlapping ones which might define an essence.
P.34 Feser’s explanation of how Aquinas comes to consider the good and true, etc. as “convertible” with being was helpful, as I didn't understand this before. Ultimately, though, the resultant “stretching” of these terms throughout the system becomes increasingly strained and unconvincing to me.
P.49 Feser has an excellent discussion of the problems with post-Humean thinking on causation, and the potential superiority of the “powers” viewpoint.
P.54 An interesting point is attributed to John Haldane: that indeterminism considered as resulting from natural propensities in quantum systems is in keeping with the spirit of Aristotelian view.
P.58 The doctrine of analogy seems the weakest part of Thomism to me, and repeated invocations throughout the book didn’t alter my initial view on this.
Ch. 3 Natural Theology
P.65 The First Way. Aquinas thinks no potential can actualize itself, but I would say the spontaneity of QM phenomena seems to undermine this (in the same sense that the full-strength Liebnizian principle of sufficient reason is undermined). Contingent facts might beg for explanation, but not a complete explanation in terms of prior acts. New spontaneous acts are constrained by other/prior acts but not determined by them.
I do sympathize with the quest for ultimate explanation that leads to a necessary being as the ultimate source of creative power. I think again, though, that viewing this ultimate power as external to the material world weakens the argument (in other words I don’t see again why act is prior to potency).
P.91 The Second way doesn’t seem to add much once you’ve delved into the first, and understand Aquinas’ background assumptions regarding causation. Feser here brings in a discussion of Thomas’ “existence proof” from On Being and Essence.
P.92 The Third Way’s weakness is Thomas’ presentation of contingency and necessity as temporal notions. Feser helps out by noting that if we assume an infinite expanse of time, we can bring the concepts closer to the modern conception (although he says we can and should reject the “possible worlds” account of modal concepts).
p.95 Feser notes an interesting criticism, due to J.L. Mackie, that even if individual contingent things go out of existence, a “permanent stock of matter” could persist indefinitely (and hence be “necessary”). Feser says Thomism shouldn’t have a problem with this. It’s OK if matter exists necessarily, as this doesn’t impact his argument for God specifically: all necessary things get their necessity from God. I think it still is simpler if we posit a panentheistic God which includes all raw materials in its being.
In fact, a better argument from contingency to necessity is this: there is a set of all metaphysically possible things (events, objects, worlds, whatever). The sum of all of these must exist necessarily (there can be exactly one maximal set of possibilia).
P.100 The Fourth Way. This is weak: it relies on the convertibility of the transcendentals and the doctrine of analogy. These are Aquinas’ most questionable tools.
I would be tempted by a version which said there must be a maximal being in the sense of all-encompassing.
P.116 The Fifth way. This is very weak IMO. If things have final causes, then one could argue there must be a greater power underlying these (as in the first or second ways), but then here he states it must be intelligent, without adequate argument.
P.120 The Divine attributes
Immutability: God as pure Act not justified in my view, therefore God is better seem as the sum of all that is changing and unchanging (so not immutable).
Powerful: Yes, as the source of all power.
Intelligence: No argument given. Obviously, His being includes all beings which we do consider intelligent. But human intelligence is an aspect of being a finite agent in a larger context or environment. God has no larger context, so I’m not comfortable invoking analogy and calling God intelligent (or possessing a will – that’s another notion linked to intentionality which presumes an environment).
P.125 To beat a dead horse, the Thomist doctrine of analogy is an all-too-flexible tool which attempts to build a bridge from the necessary being of metaphysics to the God of tradition.
Good: Is God good? Here we are stretching the convertible sense of Good into the moral sense of good. This is difficult. It makes sense that God is the source of moral facts, alongside all others, but like the discussion of intellect, this doesn’t suffice for the N.B. to earn the human-derived label.
Simplicity. To be charitable, maybe the idea that God has infinite parts leads to a sense of simplicity (?)
Ch. 4 Psychology
P.132 The discussion of the soul I find unconvincing: thanks to science we now know that nature is continuous is a way Aristotle and Aquinas couldn’t appreciate. While I might concede that living things seem to have a “form” different from everyday non-living objects which still begs for a fuller explanation, there is no motivation for a qualitative difference between humans and our living cousins. The degree of our intelligence does distinguish us from other species, but not qualitatively.
P.151 Likewise, the discussion of immateriality and immortality is unconvincing. Knowledge of universals is not sufficient to demonstrate immateriality of mind; immortality is argued based on the doctrine of asymmetry between act and potency, which we discussed above. Was this asymmetry supposed to be an intuitively obvious axiom? If act and potency are not symmetric, I can picture potency having priority as easily (or with as much difficulty) as the reverse.
P.165 Feser presents a good diagnosis of the modern mind-body problem and the virtues of Aristotelian ideas. Good advocacy of hylomorphic dualism (excepting the idea that the human form is special vs. other living things)
The banishment of intentionality and qualities from nature and substitution of an inert material world is the source of the post-Cartesian conundrum. If, instead, these are ubiquitous features of the natural world, we are a long way toward solving the problem of mind.
P.176 Briefest part of the book is the short introduction to ethics and natural law. Some good ideas here, but of course the interpretation of good as natural inclination is difficult to work out. There is again a stretching of the sense of “good”.