This chapter opens with the discussion of vital unity, a problem at the intersection of medicine and philosophy. Broadly speaking, medicine is concerned with the preservation of a living whole, but for many ancient thinkers, like Galen, the practice of medicine was informed by a highly theoretical understanding of the relationship between the parts and the whole. The first section of the Introduction sets out the key preoccupation of the study: Galen’s understanding of the role that different body parts and systems have in maintaining the functioning of the living whole. Subsequent sections contextualise Galen’s work within the phusiologia tradition, as well the debate between empiricism and rationalism, and briefly outline key classifications to be discussed in later chapters, before turning to the content of individual chapters, situating the present study within the existing scholarship and, finally, briefly explaining how this work approaches the much-debated problem of the substance of the soul.

This introduction establishes the overarching claim of this book: that Elizabethan and Jacobean dramatists consistently focus on the disastrous consequences of willing and will-making, while simultaneously emphasizing the vital role that wills played in defining one’s sense of identity and self-worth. English Renaissance drama can be understood, in one way, to be preoccupied with considering the influence that wills exert over human life.

Here, I provide an overview of how both the faculty of the will and the last will and testament were conceived of in the period. The will was primarily thought to be an unruly part of the soul that hinders our ability to achieve what we desire, though the performance of the will was not merely localized to the body or psyche. One way of enacting one’s will upon the world was achieved for some through the production of a last will and testament. Last wills acted as tools for testators to impose their will upon the living, dictating who will, and who will not, benefit from their death. In their immaterial and material forms, wills shaped the quality and conditions of one’s life and afterlife.

This chapter explores Marcus’ concept of the soul and its main cognitive parts (hēgemonikon, nous, dianoia, daimon) and their relevance for the construction of a concept of the self that is closely interwoven with Stoic self-care. It also investigates Platonic influence on Marcus’ concept of the mind and its relation with the body. Selfhood, understood as an entity referring to itself, unfolds around the hēgemonikon and, to a lesser extent, the dianoia. Self-reference by cognitive acts is limited to the logical soul. These three rational elements are subordinated to the ‘I’ (or psychagogic subject) and serve as objects of its psychagogic self-(trans)formation, thereby construing its selfhood. The perfect starting point for mental self-transformation in Marcus is hypolēpsis ‘assumption’, a single mental act, similar to Epictetus’ prohairesis ‘choice’, to which Marcus’ concept of mental selfhood is heavily indebted. Platonising rhetoric supports the delineation and detachment of the soul’s rational part (esp. nous) from external entities and subordinate mental phenomena but offers no evidence for a dualist psychology or metaphysical concept of the mind. Instead, Marcus’ concepts of mind and body abide by Stoic orthodoxy and its materialist monism.

In the third chapter, I focus on the concept of self-motion, which is tied to the definition of soul in Plato. Aristotle famously criticises this view in De anima 1.3, showing that the soul is unmoved. I offer the first lengthy discussion of Proclus’ repudiation of Aristotle’s criticism which differs from other Neoplatonist responses. Most importantly, I demonstrate how Proclus develops his own views on self-motion by using Platonic and Aristotelian insights.

The second chapter concerns the origin of motion in the universe. While Plato assumes a self-moving soul as origin, Aristotle posits an unmoved intellect. Proclus brings these two views together by regarding the unmoved intellect as ultimate source of motion and the self-moving soul as an intermediary entity. I demonstrate that his harmonisation effort goes beyond previous Platonist attempts due to the philosophical reasoning he provides. I also defend Proclus’ assumption of both unmoved intellect and self-moving soul as sources of motion against concerns brought up in scholarship.

The chapter develops the question (raised in Chapter 4) about the precise way in which soul is supposed to play the role of the primary explanans of perception. It does so by bringing out the key difficulty that Aristotle faces and by analysing the three possible answers to this difficulty. The problem is that Aristotle seems to commit himself to three jointly inconsistent tenets: (i) the perceptive soul is the primary cause of perception; (ii) perception is passive; and (iii) the perceptive soul is impassive. These claims are inconsistent if it is true that (iv) there is no way for the soul of being the primary cause of φ-ing other than being the proper subject of whatever φ-ing consists in. Two dominant ways of resolving this problem, since antiquity, consist in denying Aristotle’s commitment to either (ii) or (iii). I argue that difficulties, both exegetical and philosophical, faced by each of these strategies are insurmountable. The third possible strategy starts from denying (iv). I trace such a strategy to the medieval idea of a sensus agens and argue that although the existing medieval (and later) versions cannot stand as such, the third strategy is nevertheless the most promising one.

The chapter starts by outlining the version of direct realism endorsed by Aristotle. I argue that he was committed to uncompromised realism about perceptible qualities and to the view that we immediately perceive the bearers of these qualities without any need of further synthetic acts. These features highlight the difficulty of capturing the explanantia of perception. Two notions key to that endeavour are those of mediation and discrimination. The chapter provides a novel analysis of mediation (for discrimination, see Chapter 6), arguing that, for Aristotle, media are – more or less perfect – qualitative conductors. Furthermore, the chapter addresses the existing debate about what, according to Aristotle, happens in the sense organs when we perceive. I argue that the dilemma governing this debate between spiritualism and materialism (either ‘literalist’ or ‘analogical’) is a false one. Tertium datur, and this alternative turns out to be precisely the view Aristotle embraced: perception consists of a thoroughly material process, but what this process results in must not be a standing material likeness (which would mark the end of perception because like cannot be affected by like), but a dynamic ‘phenomenal’ likeness – the presence of a quality of the perceived object which remains to be precisely a quality of that object.

The chapter provides a novel account of perceptual discrimination (krinein) in Aristotle. Against the widespread view that the most basic perceptual acts consist in noticing differences between two or more perceived qualities, I argue that discrimination is for Aristotle more like sifting, winnowing on a sieve: it consists in identifying – with an ultimate authority – the quality of an external object as distinct from any other quality of the given range that the object could have. The chapter further explores how the notion of discrimination is embedded by Aristotle within his causal assimilation model of perception. I argue that the central notion of a discriminative mean (mesotēs), introduced in An. 2.11, is intended to capture the role of the perceptive soul as the controlling factor of a homeostatic mechanism underlying perception. As such the notion lays the groundwork for resolving the apparent conflict between the passivity of perception and the impassivity of the soul (as analysed in Chapter 5). The prospect is further explored in Chapter 7. The present chapter concludes by arguing that Aristotle conceives perceptual discrimination as a holistic assessment of the external object acting on the perceiver, including those of its features which are not causally efficacious.

The Introduction articulates the central question about the nature of perception and sets it within the explanatory project of Aristotle’s De Anima. What makes Aristotle’s account attractive, I argue, is that it strives to accommodate causal, qualitative, and relational features of perception. A central insight of Aristotle’s account is captured under the notion of perception as a complete passive activity, but that notion has, since late antiquity, appeared paradoxical to readers of De Anima and was, thus, systematically disregarded. The Introduction analyses the historical and philosophical reasons for this disregard. It further articulates the key dilemma pertaining to Aristotle’s view of the role played in perception by the soul: it should be the primary cause of an essentially passive and receptive activity, but it should itself remain unmoved and impassive; how can that be? Although this question has received relatively little attention among recent scholars, it is argued to be more crucial than the much-discussed issue of what happens in the perceiver’s sense organs. The final section of the Introduction outlines the argument of the entire book.

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.