I argue that Aristotle thinks of perception as veridical, and that phantasia – as a secondary motion consequent on perception – is responsible for all sensory error. I neutralize passages where Aristotle seems to countenance misperception by defending what I call an “object-oriented reading,” which holds that though Aristotle says we can make errors about the objects of perception, he is not committed to thinking that we can perceive them erroneously, as there are faculties besides perception (including phantasia) that engage with the objects of perception. According to the object-oriented reading, apparent misperception results when a false phantasia is mistaken for a perception, something that is possible due to the similarities between perception and phantasia. Nonetheless, since the faculties are distinct, perception remains veridical. I also address how this conception of phantasia can explain Aristotle’s appeals to phantasia in contexts like memory, thought, and animal motion.

In De Anima II.6, Aristotle divides perceptibles into three kinds: “special” perceptibles such as colors, sounds, and flavors, which can be perceived in their own right by only one sense; “common” perceptibles such as shapes, sizes, and movements, which can be perceived in their own right by multiple senses; and “incidental” perceptibles, such as the son of Diares, which can be perceived only “incidentally.” In this chapter, I explain what this division amounts to. First, I argue Aristotle’s distinction between perceiving something in its own right and perceiving it incidentally marks a causal distinction: what is perceived in its own right causes perception as such, while what is perceived incidentally coincides with what is perceived in its own right. Second, I argue that, for Aristotle, special perceptibles, unlike common ones, belong to homogeneous bodies on account of their chemical composition and affect sense organs along a range between contrary extremes. Finally, I explain the primacy Aristotle assigns to special perceptibles and his claim that perception of them alone is free from error. I conclude with some brief reflections on the primary/secondary quality distinction.

Aristotle's De Anima discusses the psychological causes of what he calls locomotion – i.e, roughly, purpose-driven behavior. One cause is desire. The other is cognition, which falls into two kinds: thought (nous) and imagination (phantasia). Aristotle’s discussion is dense and confusing, but I argue that we can extract from it an account that is coherent, compelling, and that in many ways closely anticipates modern psychological theories, in particular Dual Processing theory. Animals and humans are driven to pursue objects that attract us. Objects take on that power when we cognize them as valuable. If we rely on imagistic, automatic, uncontrolled processing mechanisms – Aristotle’s phantasia, which closely anticipates the modern notion of Type 1 processing – our resulting desires and actions will be impulsive. If we rely instead on rational, critical, deliberative capacities – Aristotle’s thought, which closely anticipates the modern notion of Type 2 processing – our resulting desires and actions will be reflective. Animals are capable only of the first kind of behavior; the human psyche is constituted of an animal psyche united with an intellectual one, so we are capable of both.

This chapter addresses an interpretive question about why Aristotle identifies generation, growth, and nourishment as the three distinct functions or activities of nutritive soul. Scholars typically try to explain this by appealing to the shared goal of these activities, though there is no consensus about what that goal is: Does Aristotle think that generation is a way of keeping oneself alive (and thus that the shared goal is self-maintenance), or is nourishment really a quasi-generative activity (and thus that the shared goal is “form (re)production”)? Rather than taking that approach, Gelber offers a different but complementary way of accounting for the unity of these activities, by focusing on the continuity of their shared physiological basis. As it is argued here, the fact that these biological processes form a continuous cycle stems from Aristotle’s adherence, in his biological theory, to principles from his hylomorphic metaphysics. Attending to the details in works such as Generation of Animals that focus on the mechanisms underlying generation, growth, and nourishment, it is shown how we can construct a coherent account of the unity of the three nutritive soul activities.

I present an overview of On the Soul, Aristotle’s investigation into how psuchē (soul) explains biological phenomena in a unified way. This principle serves as a final, formal, and efficient cause of living activities. Soul needs specific consideration because it is a unique sort of form. It is responsible not just for giving living things their capacities, but also for when and how they exercise these capacities. Soul orders the ways in which living things grow, reproduce, move, and cognize the world. It accounts for all the more specific capacities and activities of the living thing. Studying soul thus gives Aristotle the opportunity to make some of his most subtle distinctions about kinds of capacity and activity. Aristotle’s discussion of soul as cause also prepares the way for considering how it works together with body, as Aristotle does in the Parva Naturalia and biological works. I then present synopses of the chapters in this guide and discuss how they relate to one another.

I examine the status of Aristotle’s science of soul and argue that it is trans-generic in the way that Aristotle's universal mathematics is. For just as the branches of the latter differ considerably, so too do the sciences of life: botany, zoology, psychology, and (in Aristotle’s view) astronomy and theology. Discovering the correct definition of soul, which is their starting point or first principle, as with other scientific starting points, involves both induction and dialectic. Induction uses scientific observation of living things to move toward this starting point. Dialectic enables the scientist to assemble endoxa, or reputable beliefs, that allow us to solve each puzzle (aporia) that clouds our understanding (nous) of the starting point that induction enables us to reach.

Aristotle maintains that defining nous requires first defining its activity, which requires first having considered its objects, intelligible beings. This chapter is about the nature of these objects: what about them makes them intelligible? My principal proposals will be that what makes them intelligible is that they are separate or unmixed, and that because, insofar as they are intelligible, they are, in their essence, activity. I am not unaware that this makes it sound as though Aristotle takes intelligibility to consist in some kind of nous. But he himself virtually says as much, when he claims that nous is the form of its objects (lit. εἶδος εἰδῶν); besides it is a result he is committed to by the doctrines that nous is intelligible and that there is something that intelligible objects all are in common; for the alternative, as he himself says, is to suppose that nous “will have something mixed-in, which makes it intelligible just like the rest.” The challenge, then, is not to steer clear of this result, but to make sense of it. My proposal will be that the key lies in realizing that and why Aristotle thinks intelligibility is a creature of nous.

In DA I.2–5, Aristotle offers a series of critical discussions of earlier Greek definitions of the soul. The status of these discussions and the role they play in the justification of Aristotle’s theory of soul in DA II–III is controversial. In contrast to a common view, I argue that these discussions are not dialectical but philosophical. I also contend that Aristotle does not consider earlier philosophical definitions of soul to be endoxa, but rather contradoxa – beliefs about which the many and the wise disagree among themselves. Through an analysis of Plato’s and Empedocles’s definitions of soul, I show that these definitions are nevertheless treated by Aristotle as potential scientific principles for explaining two of the soul’s per se attributes: causing motion and cognition in animate bodies. The main role of the critical discussions in DA I.2–5 is to show that all such earlier definitions of soul fail this explanatory task. Nevertheless, I show that these chapters are not wholly aporetic. Aristotle makes progress by solving two scientific puzzles within them: whether the soul has spatial parts, and whether ‘soul’ refers to a uniform entity across biological species.

This chapter first argues against the widely accepted “mentalist” interpretation of Aristotle’s conception of the perception of external objects. On that view, the perception of objects results from an act of synthesis of the diverse perceptual input provided by the different sense modalities. I argue that Aristotle’s conception of perception does not require such mental “construction” of external objects. For him, we unfailingly perceive external objects by way of modally specific perception: perception without qualification is primarily of external 3-D objects, while modally specific perception is of perceptual qualities. As the special senses cannot operate in isolation from the perceptual system as a whole, it follows that we see colors, hear sounds, etc., and thereby perceive the objects whose colors and sounds they are. The second part offers a causal interpretation of Aristotle’s definition of perception as “reception of the form without the matter,” according to which the causal history of sensory affection fixes the content of the resulting act of perception: perception is cognitive in virtue of being the matterless presence of external things’ qualities in the perceiver.

I examine Aristotle’s reasons in DA I.3 for rejecting the claim that understanding (nous) is a magnitude (megethos), an idea Aristotle associates most explicitly with Plato, who describes nous as a self-moving circle in the Timaeus. Aristotle shows that his definition of soul, on which soul is not a magnitude or body of any kind, can explain perception, thought, and motion better than his predecessor’s materialist accounts. But unlike perception and motion, nous is not actualized through the body nor does it have a bodily organ, which makes nous a very different kind of soul capacity. Earlier thinkers, including Plato, already maintain that nous does not have a bodily organ, but they cannot explain how nous could operate or be a mover without being some sort of body itself. Even in the Timaeus, nous is described as being a kind of magnitude. But if nous were a magnitude of any kind, Aristotle claims it would not be able to think or reason. There is something about being a magnitude qua magnitude that makes reason impossible. His critique of Plato in I.3 prepares the way for his account of nous in DA III.4.

The phenomenon of reflective awareness, i.e., perceiving that we perceive, has often been at the center of Aristotelian scholarship, whereas that of perceptual attention, i.e., focusing on something we perceive, has been much less studied. I examine in parallel the textual evidence for these phenomena and offer a concurrent analysis of them in order to understand better how Aristotle conceives them. I argue that the Aristotelian notion of the common sense lies at the basis of the explanation of perceptual attention as much as of that of reflective awareness. In the former case, the common sense perceives the special or common perceptible that it pays attention to in its own right, whereas in the latter case it perceives the act of perceiving coincidentally along with the respective special or common perceptible. Following Aristotle, the Peripatetics defended the view that the phenomenon of reflective awareness is due to the common sense, but paid no heed to perceptual attention. On the other hand, the Neoplatonic commentators conflated the two phenomena and explained both of them by postulating either a rational character of the senses or an attentive part in the rational soul.

According to Aristotle, the three main varieties of soul – nutritive, perceptual, and rational – are hierarchically ordered. I develop and defend an interpretation of the soul’s unity that centers on Aristotle’s attempt to explain this hierarchy’s organizing cause. Aristotle draws an analogy between this series of souls and the series of figures. I first elucidate the fundamental feature both series share: each series’ prior members are present in capacity in its posterior members. I do so by examining several other cases – mathematical, biological, and physical – where Aristotle appeals to presence in capacity. I then argue that an organism’s living body is continuous by nature. That is, an organism’s soul is the principle, cause, and end of a single, articulate activity of living and each of an organism’s vital bodily movements are aspects or partial manifestations of this unitary, natural activity. This account of natural continuity is, I contend, the key to understanding what it is for one soul to be present in capacity in another. And this account of presence in capacity is, I contend, the key to understanding what it is for a soul that comprises parts to be a unity.

This chapter explores a variety of philosophical engagements with Cicero in the long eighteenth century, with particular attention to the varied, and at times contradictory, purposes that Cicero might serve. Following an introductory discussion of Cicero and John Locke, the chapter proceeds thematically, turning first to Cicero and eighteenth-century ethics, then to eloquence, civil religion, and law, and finally to Cicero’s status as an exemplar of the active life. In exploring these themes, the chapter deals with the Earl of Shaftesbury Anthony Ashley-Cooper, David Hume, Jean-Jacques Rousseau, Adam Smith, Montesquieu, John Adams, James Wilson, and Immanuel Kant.