Feser begins with the topic that deals with the foundation and nature of reality, metaphysics. Feser stresses the importance of understanding Aquinas’s metaphysic since it is the crucial building block for the rest of Aquinas’s works in natural theology, psychology, and ethics (9). To introduce the concept of act and potency, Feser begins with an illustration of a red rubber ball. One must first note the ways in which the ball actually is, i.e., how the ball is “solid, round, red and bouncy” (10). These, Feser says, are “different aspects of its “being” (10). Now, one must consider the ways in which the ball potentially is. The ball could be a different color, say green, if one wished to paint it, or it could be “soft and goey (if you melt it)” (10). The way the ball actually is, is referred to as actually or act, and the way the ball potentially is, is referred to as potentiality or potency (10).
Next, Feser notes the distinction between act and potency and how change is possible. Potency, in itself, cannot cause change since it is simply potential; it technically doesn’t exist. Feser returns to his illustration of the ball and he explains how the potential goeyness of the ball doesn’t cause the ball to become goey since the goeyness doesn’t exist yet, but it’s the application of some external force or influence--such as heat--that causes the potential goeyness of the ball to become actual (10). We see this when we see the ball melt when it’s heated. As a result, Feser concludes that “change just is the realization of some potentiality” (10). One objection that Feser responds to is one where anything has the “potential” to do anything such as the ball having the potential to “bounce to the moon” (10). However, Feser adds the qualification that “the potentialities that Aristotle and Aquinas have in mind are ones rooted in a thing’s nature as it actually exists, and do not include just anything that it might ‘possibly’ do in some expanded sense involving our powers of conception” (11).
Next, Feser indicates how a thing’s potency can only be actualized by some external for or influence, i.e., something else that is actualized (11). Feser cites the Aristotelian principle “whatever is moved is moved by another,” where “move” or “motion” is a general term that also encompasses change (qtd. in Feser 11). Lastly, there is an asymmetric relationship between act and potency, namely that act can exist without potency but potency cannot exist without act, since, to use Feser’s illustration, potential goeyness doesn’t just hang out when there is not anything to be goey; There needs to be some thing that is actualized for there to be a potential (12).
Hylemorphism is the doctrine that “the ordinary objects of our experience are composites of form and matter” (13). In fleshing this out a bit, Feser makes use of his red rubber ball once again. The rubber ball is made up of matter, which is the rubber, and form, which is the “form of a red, round, bouncy object” (13). Feser observes how the matter itself cannot be the ball because it can take the form of different objects. Similarly, the form by itself cannot be the ball since form is an abstraction (13). In describing how things change, Feser mentions how Aquinas refers to two types of change: change in accidents and change in substance (13). The former has to do with when a non-essential feature is change, such as when a ball is painted a different color, it still remains a ball. The latter has to do with when an essential feature is changed like “when a ball is melted into a puddle of goo and thus no longer counts as a ball” (13). Now, Feser explains how forms can exist in material and immaterial substances; Forms without matter are immaterial substances, and material substances, as we saw earlier, are a mixture of form and matter. Here Feser observes the same asymmetric relationship visible in act and potency. He notes, “just as act can exist without potency even though potency cannot exist without act, so too form can exist without matter even though matter cannot exist without form”. (15)
Feser now turns to one of the most important aspects of Aquinas and Aristotle’s metaphysic besides act and potency, the four causes--material, formal, efficient, and final. Utilizing his simple illustration of the rubber ball, Feser briefly and succinctly breaks down the four causes:
The material cause or underlying stuff the ball is made out of is rubber; its formal cause, or the form, pattern, or structure it exhibits, comprises such features as its sphericity, solidity, and bounciness. In other words, the material and formal causes of a thing are just its matter and form, considered as two aspects of a complete explanation of it. Next we have the efficient cause, that which actualizes a potency and thereby brings it into being ... Lastly we have the final cause or the end, goal, or purpose of a thing, which in this case of the ball might be to provide amusement to a child. 
Essence and Existence
There are about four main points that Feser makes about essence and existence. First, Feser deals with what essence is, namely that the essence of something is simply “that which makes it the sort of thing it is” and it can only be grasped by our intellect (24). For example, Feser illustrates this with our grasping of triangularity. When one grasps triangularity, one grasps the essence or nature of a triangle (24). Second, there are two things that can be said about natures or essences. One is that the nature or essences of things exist in the thing themselves like how human nature exists in individual humans, and the other thing that can be noted is that humanity, as an abstract universal, exists within the mind and it can “be applied to many individuals” (27). Third, to distinguish between different material objects, such as a tree, and its essence and matter, Feser notes how there are two distinctions in matter: common and designated matter. The former describes the matter that is common to all trees since it’s part of the nature of trees, and the latter is what “individuates one tree from another” (28).
Now what about angels? Feser discussed earlier how material substances contain matter and form, but angels are immaterial, and thus cannot be made of matter and form. Feser suggests that in this case the angel involves its “form or essence being conjoined to what Aquinas calls an actus essendi or ‘act of existing’” (29). Now Feser turns to a crucial distinction between essence and existence. To highlight this point, Feser refers to the mythical figure known as the phoenix and how one could know the nature of the phoenix, namely that it’s a “bird that burns itself into ashes out of which a new phoenix arises, without the phoenix actually existing (29). One could know the essence of something without the thing actually existing, and thus its “act of existing (if it has one) must be distinct from its essence” (29). Feser observes the importance in this distinction by Aquinas’s argument that if essence and existence were not distinct, that is, then “they would be identical” and something would have to have existence as its very being. However, God is the only exception to this, and thus God would be considered a necessary being (30).
Feser moves briefly to a discussion on the transcendentals, which he defines as "something above every genus, common to all beings and thus not restricted to any category or individual," and they include, according to Aquinas, "thing, one, something, true, and good" (33). Each of these transcendentals are convertible with each other, meaning it refers to the same thing in different ways or names. One example that Feser lists in this regard is how "Superman" and "Clark Kent" refer to the same individual (33). One can also think of other examples such as Batman and Bruce Wayne, or a female being a wife and a mother.
Feser returns to two aspects of the four causes in hopes of emphasizing their importance in Aquinas’s metaphysic, and in properly understanding the reasoning behind the 5 ways. Feser spends a good amount of space addressing contemporary objections and mischaracterizations of final and efficient causality. One in particular is the objection that because modern science has shown Aristotelian science to be wrong and faulty, thus Aristotelian metaphysics is just as useless and faulty (38). However, Feser points out that this is faulty thinking and rests on a non-sequitur. To put it simply, Feser says that “there is no essential connection between the metaphysical notions and the scientific examples” (39) There is one crucial point that Feser stresses with regards to efficient and final causation: efficient and final causation work hand in hand, and thus “we cannot make sense of efficient causation apart from final causation” (43). Feser lists many examples from modern biology, chemistry and psychology that shows how final causality is as “real and objective a feature of the natural world as Aristotle and Aquinas took it to be” (51).
Now Feser turns to explaining efficient causality a bit more in-depth, and he focuses on the principle of causality and Hume’s objection to it, as well as Hume’s problem of induction and how efficient causality dissolves this problem when properly understood. Feser explains that the principle of proportionate causality is “a cause cannot give to its effect what it does not have itself, whether formally, eminently, or virtually” (52). Feser notes how Hume thinks things can come into being, uncaused, out of nothing since one could easily imagine something popping into existence. However, the issue with this is that it’s false to think that to “imagine something is the same as to conceive of it” (53).
With the metaphysics chapter covered and hopefully understood, the rest of the book rests on this foundation, especially natural theology. Before presenting Aquinas’s five ways, Feser emphasizes that the five ways are simply summaries of the arguments that were “never intended . . . to stand alone” (62) and they ought not be divorced from Aquinas’s metaphysical ideas. Feser reveals how many of the objections raised against the five ways are based mainly on misunderstandings. For instance, some object that the second way claims that everything has a cause and thus God must also have a cause. However, Feser points out that Aquinas makes no such statement. Aquinas holds that “that which comes into being, and more generally that which is contingent, must have a cause” (65). Without exploring the details of how Feser explains the first way, Feser himself offers the gist of what Aquinas is doing in the first way. Remembering the act and potency distinction--act can exist without potency but potency cannot exist without act--Feser boils down the first way to the fact that “only what is itself already actual can actualize a given potency, and therefore (given that motion is just the actualization of a potency) ‘whatever is moved is moved by another’” (68).
For those who are not familiar with Thomas Aquinas’s first way, Aquinas essentially argues for a first unmoved mover since whatever is moved (changed) is moved by another, and there cannot be an infinite regress of motion (or change). Thus there must be a first unmoved mover which Aquinas states is God. Feser, however, adds a few qualifications to Aquinas’s argument. First, the argument is not meant to show a first “in order of time” but a “being most fundamental in the order of what exists” (69).
Second, Feser points out how there are two types of “series of efficient causes” that must be explained: the causal series per accidens and causal series per se (70). The former has to do with causal activity where a member doesn’t depend immediately on other members of the series. For instance, Feser uses the series of “Abraham begetting Isaac, Isaac begetting Jacob, and Jacob begetting Joseph” (70). While Isaac may have needed Abraham to come into existence, once Isaac grows up, he has the power of begetting Jacob regardless of Abraham being around or not. Whereas in a causal series per se, the causal activity of a member depends essentially on the activity of previous members. Here Feser uses the example of a leaf that is being moved by a stone, which in return is being moved by a staff, which itself depends on the hand (70). The movement of the leaf depends essentially on its previous members, and if any of the previous members stop, then the leaf stops as well.
The second way is a proof from causality where Aquinas argues that there cannot be an infinite series of efficient causes, and thus there must be a first efficient cause which one would take to be God. The important thing to note is that Aquinas refers to a causal series ordered per se, rather than per accidens (83). One objection that Feser highlights is one that comes from none other than David Hume. Hume argued that each cause in a causal serious can be explained by “appealing to an earlier member” and thus there’s no need of a first cause since that can always be explained as well (88). Feser points out that this objection fails because the causality that’s being used in the second way is per accidens, and as mentioned earlier this argument depends on a causal series ordered per se.
Feser summarizes the third way as “the world of contingent things could not exist at all unless there were a necessary being” (91). However, the concepts of “necessary” and “contingent” that are used in contemporary philosophy, that of possible worlds, are not the kind that Aquinas holds to, and this can be seen in the most common objection leveled against the third way (91). Feser explains how it is suggested that “Aquinas commits an obvious fallacy when he claims that ‘that which is possible not to be at some time is not,’ for even if it is possible for something to go out of existence, it simply doesn’t follow that it will actually do so” (91). In short, this objection doesn’t work since Aquinas doesn’t mean the “possible not to be” in terms of the existence in possible worlds, but he means to say that the thing that is possible not to be is to say that it “[has] a tendency to stop existing” or is “impermanent” (92). To say something is necessary, Feser explains, is to say that something is “everlasting, permanent, or non-transitory” (93). Thus, the third way is immune to the most common objection leveled against it. Feser goes into much more detail explaining the argument and how one arrives at the conclusion, however there is not enough space to explain everything here.
The fourth way is an argument that refers to a type of standard, or what Aquinas refers to as a maximum. Basically, Aquinas notes how there is a relation between other beings with regards to things such as goodness. There are some that are more good than others. Aquinas notes that things can only be more or less good when they are compared to some sort of standard or maximum. So the “maximum within any genus is the cause of everything in that genus” (100). Feser takes Aquinas’s example of fire and notes how “fire, which is the maximum of heat, is the cause of all hot things” (qtd. in Feser 100). Thus, Aquinas concludes that there must be a cause of “being, goodness, and every other perfection” (qtd. in Feser 100). Feser briefly goes into a discussion of the Platonistic implications of this argument, and concludes that Aquinas was not a Platonist but a “moderate realist” that believed the “forms of things [exist] in the things themselves, and [they exist] in a universal and abstract way only in the intellect” (103).
At last, the fifth way is an argument from finality where Aquinas argues that there is an intelligent being “by whom all natural things are directed to their end; and this being we call God” (qtd. in Feser 110). Aquinas’s fifth way, which is essentially a “metaphysical demonstration,” is a teleological argument that presupposes the existence of final causality in the natural world (110-112). Feser highlights one important factor, namely that there are chance events and it’s wrong to think that “everything” has a final cause like thinking that mountains have a final cause. Rather, things have a final cause insofar as “such natural processes embody patterns of efficient causation that are themselves intelligible only in terms of final causation” (114). When one understands final causality well enough, one can easily grasp the logic behind the fifth way and see its strength.
In the psychology chapter, Feser makes it a point in mentioning how modern philosophical problems with philosophy of mind--such as the mind-body problem--were not present to Aquinas’s day. Consequently, Feser suggests that the problems that plague contemporary philosophy--mind-body, other minds, and the mind reality gap to name a few--are a direct result of abandoning a “hylemorphic conception of the world for a mechanistic one” (132). Now, to understand what the soul is one must recall the doctrine of hylemorphism spelled out earlier. With that, Feser explains how the soul is simply “a specific kind of form which makes the body a living thing” and “makes the difference between living and non-living things” (132).
Because of the Cartesian conception of the soul--where the soul is a completely separate substance apart from the body--many individuals have trouble grasping the Aristotelian view without confusing it with Descartes’ view. Feser makes it clear that Aquinas and Aristotle do not see the soul as some immaterial substance or some weird thing that humans have, but it’s simply “one kind of form among others” (134). There are three types of souls from the Aristotelian point of view: the vegetative soul, which is responsible for “taking in nutrients, growing, and reproducing itself” (137). The animal soul, which in addition to having the powers of the vegetative soul, has the “powers of sensation, of locomotion and of having the sorts of appetites associated with sensation and locomotion” (137). And the third type of soul is the human rational soul, which has the powers associated with the vegetative and animal soul, and in addition has the “distinctively human powers of intellect and will” (138).
Next, Feser turns to a discussion on the intellect and will. An understanding of final causation is important here since Feser explains how the final cause or end goal of the intellect is truth, and the final cause of the will is “to choose those courses of actions which best accord with the truth as it is discovered by the intellect, and in particular in accordance with the truth about human nature” (142). In exploring the nature of the intellect, Feser explores the way in which our minds or intellect grasps concepts and objects, and as a result concludes that “when the intellect understands something, it grasps its form” and the form of the thing in question “exists both in the intellect and in the thing itself” (148). Consequently, the problem that many of the modern philosophers had, namely trying to fill in the gap between our mind and its understanding of reality, dissolves entirely.
The will, according to Feser’s interpretation of Aquinas, is “a power to be drawn towards (or away from) that which is apprehended by the intellect” (149). On this account, Feser observes how it follows that anything without intellect will not have free will (149).
Feser then returns to a discussion of the soul and hylemorphic dualism. The intellect, Feser suggests, is immaterial and not dependent on the body at all for its function. Feser notes two main arguments that Aquinas gives in support for this, however, only one will be focused on. The first is that the intellect is able to grasp any form and is not limited in the types of natures it can grasp. Thus the intellect must “not depend on the operation of any material organ” (153). Essentially Aquinas, according to Feser, says that “when the intellect grasps the form of a thing, it is necessarily one and the same form that exists both in the thing itself and in the intellect” (153). When one thinks about a green round table, the same form of roundness and greenness that exists in the table is the same form that is grasped by the intellect. When one is staring at a brand new silver square MacBook Pro, the form of squareness and silverness that is in the MacBook Pro is the exact same form grasped by the intellect.
Feser makes an interesting point. If it were the case that the intellect were somehow material and if the form that is grasped by the intellect is the same form that is in the thing, then it would follow that the intellect, which we could say is your brain, would have to change shapes whenever one things about something (154). When one thinks about the green round table, then that specific part of the brain where the intellect is located would change into a green round table. Same goes with the MacBook Pro. In addition, one cannot think about multiple forms at once because that would entail that if one thought about the green round table and the MacBook Pro, the part of the brain that is the intellect would change and both be a green round table and a MacBook Pro, at the same time, which is clearly absurd (154). As a result, Aquinas’s view attempts to demonstrate that it is metaphysically impossible to view the intellect in a materialistic way (157).
Feser ends the psychology chapter by addressing some of the problems in contemporary philosophy listed earlier, and showing how Aquinas’s hylemorphic dualism is immune to these issues. For example, the mind-body problem so commonly associated with Cartesian dualism is not at all an issue for Thomistic dualism. Reason is, as Feser points out, the conception of the mind and body is wrongheaded in the first place since it “lies in the false assumption that the relationship between soul and body is to be conceived of as an instance of efficient causation between two complete substances” (166). Rather, the hylemorphic view helps one see that the relationship between soul and body is “an instance of formal causation relating two components of one complete substance” (166 Feser’s Emphasis).
In the chapter on ethics, Feser focuses on three main areas: the good, natural law, and religion and morality. While ethics today appears to be detached form metaphysics, Aquinas’s theory of natural law and the good flow directly from his metaphysic. Before continuing with Aquinas’s view on the good, Feser addresses Hume’s conclusions that one cannot derive an ought (statement of value) from an is (statement of fact), also known as the naturalistic fallacy (175). Another major perk of the Thomistic metaphysical system is that there is no fact value distinction, and thus no fallacy because “‘value’ is built into the structure of the ‘facts’ from the get-go” as a result of being built upon a teleological conception of the world (175).
Feser explains how there are particular ends that are in accord with each and every organism or substance, and one must realize and reach these ends in order to properly “flourish” as the organism or substance one is (177). An oak tree, for instance, is good to the extent that its roots properly develop to be strong and long into the ground. Otherwise, if its roots do not develop properly, then the oak true is said to be bad (177). As a result, there is a standard of goodness that appears here. Now the subject turns to human beings; Human beings have certain ends that are inherent with our nature as rational beings.
The most basic principle of Aquinas’s natural law is that “good is to be done and pursued, and evil is to be avoided” (qtd. in Feser 183). Feser explains that basically everyone seeks to do what is “good” and avoids what is “evil”, even if what that person deems as “good” is questionable (184). For instance, for a thief it would appear to be “good” if he robbed thirty different people so that he becomes wealthy, and it would be “bad” if he could not avoid being caught by the authorities. In a loose sense, each person at least seeks to pursue some sort of good and avoid what is bad. So what is the good then? Basically, anything that one does that allows one to flourish according to its nature is good, and anything that one does that frustrates that goal is bad (184). Moreover, since it is reason that allows one to apprehend the ends that are a part of human nature, Feser observes that “good action is just that which is ‘in accord with reason’” (185).
By the level of detail included in this summary, it’s evident that Feser has a lot to say as his book is densely packed with material. Some may find themselves practically highlighting the whole book because of how rich and tightly woven the material is. Feser writes clear and straightforward enough for a laymen in philosophy to pick up this book and get through it. However, this assumes that the individual has some experience in philosophy. Thus, it’s recommended that anyone who reads Aquinas should have experience in comprehension, critical thinking, and patience. Luckily, Feser does a very good job in explaining the concepts clearly, and his illustrations are extremely helpful in digesting many of the more complex ideas, such as Aquinas’s metaphysic.
This reviewer’s hope is that many Christians will be exposed to the value of Thomistic philosophy and the advantages, as well as contributions, that Aquinas’s works make in all areas of contemporary philosophy, as well as theology. Feser’s book is definitely an excellent introduction to Aquinas’s thought, and anyone who is even remotely interested in Aquinas’s works should definitely pick this book up.
Apologetics 315 Book Reviewer David Rodriguez is a student at San Diego State University and is majoring in philosophy with a minor in biology. His primary philosophical interests include ethics, philosophy of religion, epistemology and medieval philosophy. In addition to philosophy, David has a keen interest in theology and medieval history. He is currently concerned with pursuing a career in bioethics. His webpages are www.walkingchristian.com and Ad Dei Gloriam.