In this text, of which we have translated a large excerpt, Olivi defends his own version of the identity theory of the soul and its powers. On this version, the soul is a bundle of powers (plus spiritual matter), and so is identical to the entire collection of its powers (plus spiritual matter). To defend this view, Olivi first considers and rejects another version of the identity theory, on which the soul is a single power capable of eliciting all of the different vital acts associated with a living being. His main argument against this position is that diverse forms of production or of activity require powers that are themselves diverse by nature or essence. Olivi then attacks the distinction theory developed, for instance, by Aquinas, arguing that, among other things, this theory conflicts with our conception of ourselves as essentially free and rational agents. Next, Olivi criticizes Bonaventure’s distinction theory, arguing that it is impossible for the soul’s powers to be substances and yet dependent on the soul itself. Finally, Olivi puts forward his own preferred bundle theory of the soul and its powers.

In this text, of which we have translated a large excerpt, Henry of Ghent rejects the view defended by Albert and Aquinas according to which powers are accidents distinct from the essence of the soul. Instead, he maintains, the soul is its powers “through its essence”. To show this, Henry devises an argument directed against Aquinas’ claim that a power must be in the same category as its act. The upshot of the argument is that this claim must be rejected because, along with some premises widely accepted by medieval Aristotelians, it leads to a (vicious) infinite regress. Additionally, Henry develops his own theory of the powers of the soul. While he thinks that the soul is its powers through its essence, he contends that the soul’s powers do add something to the soul, namely, relations to their acts. For example, the intellect is the soul as related to the act of thinking, whereas sight is the soul as related to the act of seeing. On the basis of this relational account Henry discusses in this text the distinction between those powers of the soul that are tied to a bodily organ, such as sight, and those that are not, such as the intellect.

In this text, Duns Scotus asks: does the image of the Trinity in the rational soul consist in three really distinct powers? His answer is in the negative. The powers of the soul, he maintains, are really the same as the soul, but formally distinct from it as well as from one another. To develop this view, Scotus first refutes several alternative theories, including Aquinas’ distinction theory and Henry’s relational account of powers. In his refutation of Aquinas, Scotus provides a discussion of the Category Argument, arguing that it confuses two distinct senses of the term ‘potency’, ‘potency’ understood as power and ‘potency’ understood as a non-actual mode of being. Against Henry, Scotus argues that the view that the powers of the soul are the soul as related to different acts entails that these powers must always be actualized. To develop his own account of the soul and its powers, based on the formal distinction, Scotus draws on the notion of unitive containment and his account of the transcendentals. He argues that the soul is explanatorily prior to its powers, arguing that it exists at a “first instant of nature” while its powers exist at a “second instant of nature”.

In this text, James deals with the question of whether the will moves itself. In order to examine this question, he thinks it necessary to first develop a theory of the soul’s powers in general. At the heart of this general theory is a (then) unorthodox view about the granularity of the powers of the soul. James thinks that there are, in addition to our generic powers to think and see, a myriad of fine-grained powers in the soul, such as the power to think about cathood or the power to see red. James does not venture to say just how fine-grained these powers are, claiming that only God knows this. Drawing on terminology due to Simplicius, he calls a generic or coarse-grained power of the soul a “general aptitude” (idoneitas generalis), while he calls a fine-grained power a “special aptitude” (idoneitas specialis). James also argues in this text that an aptitude, whether general or special, is an “incomplete act”. By characterizing a power as an incomplete act, James is claiming that it is an incomplete version of the operation that it can bring about. So, for example, Socrates’ aptitude to think about cathood is an imperfect version of his act of thinking about cathood.

In this text, Ockham deals with whether memory, intellect, and will are really distinct powers. He answers in the negative. After presenting first Aquinas’, then Henry of Ghent’s, and finally John Duns Scotus’ views in some detail, along with replies, Ockham presents his own uncompromising identity theory of the powers of the soul. Based on the principle of parsimony, he argues that the rational soul is identical to the intellect and the will. By transitivity, this entails that the intellect is identical to the will so that the rational soul is a single power to engage in acts of thinking and and willing. Fleshing out his view, Ockham also gives a sort of rule for knowing when distinct cognitive and appetitive powers must be posited, and when not. According to this rule, if everything outside of a cognizer or desirer remains the same, and the cognizer or desirer is able to have an act of one power, while being unable to have the act of another power, then those powers must be distinct. For example, some people may be unable to see while being able to hear and other people may be unable to hear while being able to see. It follows that sight and hearing must be distinct powers.

In this text, Durand rejects a common assumption undergirding much of the Latin medieval debate about the relation between the soul and its powers. According to this assumption, which we can call the uniformity assumption, all powers of the soul that bring forth vital operations, such as the intellect and sight, bear the same relation to the soul. Identity theorists maintained that all of these powers are identical to the soul, while distinction theorists held that all of these powers are distinct from the soul. Against this consensus, Durand argues that some powers of the soul are identical to the soul, while others are distinct from it. More precisely, he advocates an identity theory with respect to the vegetative powers but a distinction theory with regard to the sensory and rational powers. He motivates his identity view regarding the vegetative powers with the argument that these powers have substances as their effects and the premise that causes must be like their effects. To motivate his distinction theory regarding the sensory and rational powers, Durand does not draw on Aquinas’ Category Argument, which he thinks is unsound.

In this text, Aquinas discusses the question of whether the powers of the soul are the same as the soul. The text is part of Aquinas’ analysis of Augustine’s doctrine of the image of the Trinity. Like his teacher Albert the Great, he argues that the soul and its powers are distinct, and, like Albert, he holds that the soul’s powers are to be viewed as necessary accidents “flowing” from the soul. But Aquinas goes beyond his teacher in an important respect. He devises a new argument in favor of the distinction theory—an argument that we may call the Category Argument. The argument goes like this. A power must be in the same category as its act. All acts of the soul, like thinking, seeing, etc. are accidents. Hence, the powers of the soul must be accidents too. Aquinas justifies the major premise that a power must be in the same category as its act by appeal to what we might call a Causal Proportionality Principle. According to this principle, a cause must be like its immediate effect, where the cause is a power, and the immediate effect is its operation. The Category Argument proved very influential for the subsequent debate over the relation between the soul and its powers.

In Ordinary Question 4, of which we have translated a large excerpt, Thomas of Sutton argues that the soul and its powers are distinct. Sutton’s strategy for defending the distinction theory is, roughly, two-pronged. First, Sutton develops his own conception of power and act. Second, he aims to show that Aquinas’ arguments for the distinction theory, in particular the Category Argument, are sound, despite objections to the contrary. Key to Sutton’s own conception of power and act are two ideas. The first is that a power is a kind of possibility. Specifically, a power is a possibility that remains when it is actualized. The second idea is that powers and acts are mutually exclusive kinds of being. No act is a power, and no power is an act. Since the soul is a kind of act according to the Aristotelian view, this entails, for Sutton, that the soul is not its powers. In this text, Sutton also seeks to rebut Henry’s regress argument against Aquinas. He argues that this argument is predicated on a mistaken conception of how necessary accidents or propria relate to their bearers.

The introduction describes the scholastic Latin debate over the relation between the soul and its powers in the late thirteenth and early fourteenth century. It shows that this debate concerned the question of how a living being’s natural kind, which is determined by its soul, and its kind-specific powers are related. Is a living being’s soul the very same thing as its kind-specific powers, or is its soul perhaps something more basic upon which its kind-specific powers depend? The introduction shows that there were two overarching answers to this question in the thirteenth and fourteenth century: the identity theory, according to which the soul and its powers are identical, and the distinction theory, according to which the soul is distinct from its powers. The introduction first highlights that the debate between identity and distinction theorists already arose in the twelfth century in response to Augustine’s doctrine of the image of the Trinity. It then traces, in broad strokes, the development of the debate from the twelfth century until 1250. Finally, it discusses the phase between 1250 and 1320 focusing on the reception of Aristotle’s theory of the soul in the Latin West.

This text of Bonaventure’s gives a nice indication of how Aristotle begins to influence the debate about the relation between the soul and its powers in the Latin West around the 1250s. In this text, Bonaventure is still very much in dialogue with the earlier debate. He recounts the early twelfth-century identity theory and earlier versions of the distinction theory, and he argues in favor of the version of the distinction theory defended by early Franciscans like Alexander of Hales. As Bonaventure states this latter theory, the soul and its powers are one “in substance” but differ “in essence”, the essential difference having to do with the fact that the powers of the soul, unlike the soul itself, are relations. But Bonaventure also introduces a philosophical innovation into this theory—one that draws on Aristotle. He argues that the powers of the soul, despite being relations, are special types of substances, namely, substances “by a tracing back” (per reductionem). He understands by “substances by a tracing back” imperfect occupants of the category of substance.

In this text, Albert deals with Augustine’s theory of the image of the Trinity. An examination of this theory leads him to an investigation of the relation between the soul and its powers. Albert contends that the soul and its powers are distinct. He maintains that the soul’s powers are propria, that is, necessary accidents, and following Avicenna he claims that they “flow” from the essence of the soul. In this text, Albert also considers the identity theory, on which the soul and its powers are the same entity but rejects it because it “borders on heresy”. He argues that the identification of the soul and its powers is perilously close to the identification of essence and power in God. Finally, Albert invokes the Boethian notion of a “power-whole” (totum potentiale) to develop his own account of the soul and its powers and to make sense of the Augustinian claim that our rational soul is an image of the Trinity. Albert was one of the main defenders of the distinction theory in the second half of the thirteenth century, and his version of this theory influenced Aquinas.

In this text, Godfrey asks whether a created substance can be the immediate principle of its operation. ‘Power’ and ‘immediate principle of operation’ are synonymous terms here. Hence, the question that Godfrey raises is this: is a substance a power? Godfrey’s answer is nuanced. Like Albert and Aquinas, Godfrey adheres to the view that powers like sight and the intellect are propria or necessary accidents distinct from the soul. However, he openly rejects Aquinas’ Category Argument for the distinction theory because he finds Henry’s regress argument against the claim that a power must be in the same category as its act convincing. The regress argument also leads Godfrey to argue that there is, in addition to such powers as the intellect and sight, what we might call a higher-order power of the soul. This higher-order power is the soul’s power to bear such powers as the intellect and sight. Unlike the intellect and sight, this power to bear powers is identical to the soul, Godfrey thinks. Thus, Godfrey defends the Thomistic distinction theory; but he also makes a concession to Henry by arguing that the soul is at least one power through its essence, namely, a higher-order power.

This chapter analyzes the key notion of the “human act” (actus humanus) around which Aquinas’s action theory revolves. It argues that, for Aquinas, the general term ‘act’ is used broadly to denote any power-exercise in nature, whether in the animate or the inanimate domain. Given this broad scope of the term ‘act,’ the chapter considers, in a next step, what sets human acts apart from other power-exercises. It argues that, according to Aquinas, one differentiating feature is that a human act is a hylomophically organized composite of two power-exercises, where a volition that he refers to as “use” is the formal component and a power-exercise caused by volition that he refers to as the “commanded act” is the material component. However, as the chapter also shows, Aquinas chiefly relies on an aetiological criterion to differentiate human acts from other power-exercises, arguing that a human act is explained by a preceding act of free choice. It then shows that choice likewise displays a hylomorphic structure, for Aquinas. It is a volition materially speaking, and its form is the preferential character that this volition inherits from a preceding judgment that Aquinas refers to as the “judgment of choice.”