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.

The sixth chapter concerns the valuation accorded to theoria, both as festival-attendance and as philosophical contemplation. As the former, the activity primarily has practical benefits or instrumental value, whereas as the latter, it has primarily intrinsic value, or value in itself. For the value attached to festival-attendance concerns fulfilling a social, political role for the city, and that of sanctuary visitation is similarly instrumental, although more individual given its aim concerned with healing physical maladies. Plato and Aristotle signal a departure from the position that accords theoria primarily instrumental value. The two philosophers concur that theoria as philosophical contemplation, by nature, is an activity desired for itself and is good in itself. However, in a secondary way, Plato and Aristotle also hold that theoria-thinking produces good effects, and in this regard, their view partly coincides with the valuation connected to the traditional practice.

This chapter assess the philosophical foundation for Cicero’s views on human social relationships and community in the Roman Republic. Starting from De officiis 1.153, I argue that such a foundation is provided by the specifically Stoic notion of the community of gods and human beings, and of human beings as sharing rationality. The De officiis is then assessed on the basis of Cicero’s emphasis on the social aspect of virtue. The remainder of the chapter traces this same theme throughout Cicero’s theoretical writings (including his works on rhetoric), first in the earlier De inventione, De legibus, and De republica, and second in the De finibus and the Tusculanae Disputationes. Hence the commitment to this Stoic foundation for sociability is a constant in Cicero’s oeuvre.