In chapter 4, Feser lays the ground work for the soul, the natural law theory of ethics, and the relationship between faith and reason using the concepts he's laid down in the previous chapters. I've decided to break this review into three parts because the review became so long.
In the beginning of the chapter Feser finds room for two more insults on Daniel Dennett and Sam Harris—Dennett for "sheer speculation" on evolutionary psychological explanations of religion, and Harris for apparently being boring in his book, The End of Faith. Certainly there's a lot of speculation in evolutionary psychology, but the argument for the naturalistic origins of over-active agency detection forming the basis of god belief I think are pretty strong and well supported by evidence. Anyway, onto the soul.
There are a lot of misconceptions about the Aristotelian conception of the soul. It differs significantly from the Cartesian conception where there is a physical body and a non-physical soul that operates the body like a "ghost in the machine." Although many lay people still hold to this concept of the soul, it has severely fallen out of fashion in the relevant sciences and philosophy, and is considered by most in those fields flat out false.
The Aristotelian-Thomistic (or A-T for short) soul is different. The "form or essence of a living thing is just what Aristotle (and Aquinas) mean by the word 'soul,'" Feser explains. The "soul" is "to refer to the nature of a living thing, whatever that turns out to be," adding, "The soul is just a kind of form." (121) But what if it turns out to be that we're just complex arrangements of matter and energy governed by the fundamental forces described by the laws of physics, with no free will of our own? This is after all what science is showing us more and more everyday. It seems to me that terms like "soul" at best are a metaphor, like when we refer to the "soul" of a city, and at worst an outright metaphysical falsehood.
The soul being form and essence means all things have a "soul" on the A-T view. But there are three kinds of souls that Feser describes (121-122) and this means that for you Christians (spoiler alert!), you sadly won't be seeing your cat or dog in heaven:
Nutritive soul: a form or essence that gives a thing that has it the powers of taking in nutrients, growing, and reproducing itself.
Sensory soul: a form or essence that gives a thing that has it both the powers of a nutritive soul, and also an animal's distinctive powers of being able to sense the world around it (by seeing, hearing, etc.) and to move itself (by walking, flying, etc.).
Rational soul: includes both the powers of the nutritive soul and the sensory souls and also distinctively human powers of intellect and will: that is, the power to grasp abstract objects - namely, the forms or essences of things - and to reason on the basis of them, and freely to choose different possible courses of action on the basis of what the intellect knows.