A comparison of Aristotelian-Thomistic philosophy with contemporary theories in the philosophy of mind is a demanding project. It requires both a deep familiarity with two different fields and the ability to discern common agreement between them. Moreover, if one wishes to go further and develop a helpful tool to educate and motivate others to do the same, one must communicate these insights simply and free from jargon. Edward Feser seems to have done just this in his Immortal Souls: A Treatise on Human Nature.

At a time when reductionist views of human nature often predominate due to their explanatory power, many philosophers have felt the need to adopt such reductionism as a principle while explaining problems of consciousness. However, others – such as Feser – have taken a stand against these pressures by questioning the wisdom and soundness of such presuppositions. Bringing in Aristotelian-Thomistic philosophical principles, but not being restricted to a mere exegesis of their thought (p.5), Feser engages in a fresh dialogue between ancient and modern philosophy. The result is spectacular: the Aristotelian theory of hylomorphism is shown not to be a fictitious and useless abstraction but instead, the most complete way to explain the whole experience of human nature as a body–soul composite, even after so many centuries of philosophy.

Feser is aware that to defend this position well, he must explain Aristotelianism in terminology that engages contemporary philosophers of mind. His paraphrases of Aristotle’s argumentation are generally in simpler everyday language and often supplemented with more contemporary examples drawn from everyday life. Most importantly, following a dialectical method used by Aristotle himself as well as by followers such as Aquinas, he often brings forth some of the strongest opposing views before evaluating them and proposing alternative views.

This very method is the reason why Feser is so careful to restructure his treatise on human nature from the starting point of modern and contemporary philosophers: an experience of ‘the self’ or the very activity of thinking. In so doing, he shows that this experience is in fact also affirmed and accounted for in the richness of the Aristotelian-Thomistic view of human nature. It is after he considers and responds to the objections of other philosophers who have argued for reductionism, eliminativism, imagism, innativism, etc., that he finally takes up the consideration of the bodily nature of human beings.

Many of Feser’s arguments appear to be original as well as invitingly readable. Some notable examples are: his argument against Hume’s bundle theory (pp.26–27), being able to recognize the self apart from one’s thoughts (p.45), that thought cannot be reduced to language (p.95), or how the movements of the will are associated with the emotions but differ from them (p.124).

Feser’s argument in Part I is that our sense of self, our thoughts, and our free choices are what perdure. The substance that underlies these acts is not reducible to our mental imagery, emotions, or even our neurotransmitters. Our thoughts are more transcendent and specific than anything, which can be deduced from mere correlations between the mind and the brain. In Part II, Feser rephrases Aristotelian hylomorphism with modern examples. While ‘matter’ is often understood differently in contemporary science, numerous scientists of the past have found that Aristotle’s conception is a fitting description for their theory behind the experimental phenomena. In Part III, by emphasizing the clear correlation of the functions of the mind with the body and drawing upon phenomenological insights, he argues against the Cartesian error, which entirely separates our rationality from our animality. In Part IV, he argues against a materialist error, which ‘entirely assimilates our rationality to our animality’ (p.256). Finally, he proposes his fully philosophical argument for the immortality of the soul, while also summarizing classic Thomistic arguments.

However, for maximum clarity and authenticity, if Feser intends to borrow the whole parts from the thought of Aristotle and Aquinas on the soul, this treatise could benefit greatly from a closer reading of the original texts. This is especially the case when it comes to giving an account of the internal senses, which does a lot of heavy lifting for Feser to explain phenomena common to non-rational animals and to humans or to phenomenological perceptions and their relation to embodiment (e.g., p.100). For example, Aristotle and Aquinas did not describe the common sense as a ‘synthetic sense’, as Feser describes on pp.66 and 292, but as a faculty that distinguishes different external sensibles from each other and senses that one is sensing. If the ‘common sense’ were ‘a synthetic sense’ that unifies external sensation into a ‘single, coherent conscious experience’ (p.292), this would overlap with the function of another internal sense: the cogitative power. Speaking of which, Aquinas’s ‘passive intellect’ is actually not the same as the ‘possible intellect’, as Feser claims on p.293, fn. 504. These are two different faculties. Rather, the passive intellect is the cogitative power, and Aquinas distinguishes these two clearly in his Commentary on the Sentences.Footnote ¹ Identifying one with the other seriously misconstrues the Aristotelian-Thomistic account of abstraction and would eliminate the need for the conversion to the phantasms in order to understand. If Feser had included this distinction, it would have only further bolstered his thought regarding how some sort of imagery is involved in analogous ‘beliefs’ in animals (p.255). Moreover, this also explains how, as Feser himself says, intelligible forms are not mere perceived patterns but surpass our imagination (p.292), although indeed patterns and imagery help facilitate acquisition of concepts (p.296).

Feser effectively draws on many examples from chemistry, although he verges on trying too hard to make the ancient and medieval philosophy more relevant. Applying the original examples to analogous modern phenomena often sacrifices the clarity of the original text. An example of this is describing the constant evaporation and condensation at the surface of water to describe Heraclitus’s view instead of the simpler, original example of never being able to step in the same river twice (p.174). Likewise, explaining the abstraction from phantasms using a banana (pp.292–293) seems to be a much harder case to justify than the abstraction of the universal essence of ‘animal’ or ‘body’, which are examples that are actually explained in the original texts. Most importantly, without the nuances connected to the explanation of these universal concepts, the whole process of abstraction can be caricatured as a convenient invention to just fill in the gaps.

Feser is astute in pointing out that an equivocation can be the source of much confusion and talking past one another (p.187). Indeed, the modern understanding of ‘matter’ differs considerably from the more classic Aristotelian understanding of this same term, ‘matter’. This same level of nuance should likewise be applied to other Aristotelian-Thomistic terminology, since anachronistic connotations of terms such as ‘imagery’ may also obscure the clarity of the original thought.

Nevertheless, Feser has undertaken a laudable and courageous task making some first important steps in breaking down the walls between the current schools of philosophical anthropology, while remaining himself a good disciple of the scholastic method by engaging in dialectic. Like Aristotle and Aquinas, Feser extracts the truth from his interlocutors, without prejudice as to who they are: modern empiricists, rationalists, phenomenologists, or even neuroscientists. However, Feser also convincingly shows that under closer inspection, they fall short in explaining our experience, while Feser’s Aristotelian-Thomistic view excels. The relatively minor flaws of this work therefore do not appear to obstruct its great merit as a rigorous engagement of the philosophical presuppositions behind the mass of objections that are often hurled against the theory of human beings as a body–soul unity.