This chapter turns to Karl Marx’s treatment of Epicureanism and Lucretius in his doctoral dissertation, and argues that the questions raised by Marx may be brought to bear on our own understanding of Epicurean philosophy, particularly in respect of a tension between determinism and individual self-consciousness in a universe governed by material causation. Following the contours of Marx’s dissertation, the chapter focusses on three key topics: the difference between Democritus’ and Epicurus’ methods of philosophy; the swerve of the atom; and the so-called ‘meteors’, or heavenly bodies. Marx sought to develop Hegel’s understanding of Epicurus, in particular by elevating the principle of autonomous action to a first form of self-consciousness – a consideration largely mediated by Lucretius’ theorization of the atomic swerve and his poem’s overarching framework of liberating humans from the oppression of the gods.

This paper addresses the role of first-person plural expressions in DRN. I begin by outlining some ambiguities in the Latin first person plural before going on to demonstrate how those ambiguities may function for readers of DRN. First I show how ambiguity between inclusive and exclusive uses of the first person plural allow such expressions as quod inane vocamus to be interpreted differently by readers at different stages of their Epicurean education. I then discuss Lucretius’ use of inclusive first-person plural forms to characterize his own relationships with his reader. Finally, I discuss the role of collective first-person plurals in the argumentation of the poem, and its implications for Lucretius’ avowed empiricism. A central aim of the paper is to show how the ambiguities inherent in the language of Lucretian didaxis allow for different responses by different groups of readers.

The idea that the universe is infinite in size is central to the Epicurean system. Infinity, however, is also a concept that, in the history of philosophical, scientific and artistic discussion before and after Lucretius, has defied explanation, engendered paradox, and stimulated the romantic sensibility. This chapter looks at the strategies, philosophical and literary, deployed by Lucretius to achieve closure on this inherently open topic. Co-ordinate with the relationships of analogy and complementarity between the text of the DRN and the nature of the universe it describes, the poem’s poetics of closure and enclosure, on the one hand, and of non-closure or ‘false closure’, on the other, express and enact the infinity of the universe conceived both as all-encompassing and as open-ended. These rival conceptions of infinity are modeled throughout the poem, and especially in Epicurus’ triumph of the mind (1.62–79) and Lucretius’ reworking of a thought-experiment attributed to Archytas of Tarentum (1.951–83). Taken together, they bring out the tension, or complementarity, in Lucretius between the totalizing scientist who prescribes an intellectual panacea and the sublime poet who reaches into the beyond.

In Alexandria at some point in the early third century bc, Herophilus of Chalcedon identified the nerves as a distinct system within the body, traced their origins to the brain, and recognised their role in transmitting sensation and voluntary motion. His discovery was based on dissection and vivisection, not only of animals, but also of human beings. Herophilus’ younger contemporary Erasistratus also integrated these findings into his rather bolder physiology. The implications of this discovery were of course wide-ranging. From a modern perspective, it is now widely celebrated as having established, for the first time on something like a scientific basis, that the brain has more or less the functions that we now ascribe to it. Likewise, in antiquity, Galen relied heavily on Herophilus’ discovery in his proof that the rational soul is located in the brain. As we shall see, it also had an impact on Stoic psychology. What exactly Herophilus and Erasistratus saw as its implications, however, is a different question, and the difficulties in answering it are considerable given the state of the evidence.

Galen of Pergamum (129–215 ce), the influential Greek doctor and philosopher, had much to say about the soul and its relationship to the body. In developing his views on psychophysical interaction, Galen used and combined ideas and concepts derived from the philosophical traditions of Platonism, Aristotelianism, and Stoicism. He also took medical views on board, ranging from the earliest fifth-century bce writings of ‘Hippocrates’, the fourth-century doctor Diocles of Carystus, and Hellenistic medical writers such as Herophilus and Erasistratus, to the works of his older medical contemporaries, such as Rufus of Ephesus and the Pneumatist writer Archigenes of Apamea; these were especially relevant when it came to the anatomy and physiology of the soul and the diagnosis and treatment of mental disorder in its somatic aspects.

In the first book of his Tusculans, Cicero gives two arguments that the soul is eternal. Specifically, he concludes that each human soul’s rational part or ‘mind’ (mens) neither came to be nor will perish. I shall argue that in pursuit of this conclusion, Cicero constructs the position that, at least in this life, the human mind does not ‘sense’ itself, but knows about itself only by inference from its ‘sensations’ of other objects. First, the question of the mind’s sensation of itself is comparable to current debates about consciousness, for example to questions relating to the ‘hard problem’ of consciousness. To put it crudely, the ‘hard problem’ is that we suppose that our minds are conscious of themselves immediately, and that what we seem to learn from this immediate self-consciousness is that our minds are so different from the natural world we observe through the senses that it is a puzzle to understand how the two could be as intimately related as they appear to be.

Throughout its long history, Stoic philosophy was subjected to much criticism, from inside the school as well as from outside. This is particularly true when it comes to psychology. Roughly speaking, the Stoic soul is characterised by two main features: first, it is defined as a single and entirely rational substance which has no parts, in particular no irrational parts as is the case in Platonic and Aristotelian theories; this psychological monism is the ground for what I will call the ‘Stoic pledge’, namely that the moral agent is absolutely responsible for all his mental acts: impressions (phantasiai) and assents (sunkatatheseis), and also passions, virtues and vices, sensations, and so on. All of these are in our power, because we always have the ability to avoid them, to have second thoughts about them, and to put them right if they are wrong.

The structure of this essay is roughly as follows. After an introduction in which I rehearse some of the main elements of Stoic physics and psychology, I set out the evidence for the Stoic doctrine that the individual soul is both analogous to the cosmic soul and a part of it, as was held by the early exponents of the school. I argue that the doctrine threatened to land the Stoics in trouble, unless they were ready to qualify it by applying to it certain distinctions. Then I consider the doctrine’s historical origins, discussing several possible antecedents of it, with a focus on a Socratic report in Xenophon and on Plato’s dialogues, and showing that the Stoics went beyond all their predecessors. After this historical excursus I turn to examine some of the arguments advanced by the early Stoics to prove that the cosmos has a soul, including one which compares the relation between the cosmos and individual human beings to that between a father and his offspring. This leads me to analyse in more detail this comparison which occurs also in other contexts and is sometimes problematically connected with the notion that the individual soul is a part of the cosmic soul. One of the texts which are relevant to this issue, a report in Sextus Empiricus, is the object of a separate discussion in the final Appendix.

The relationship of soul to body was one of the earliest and most persistent questions in ancient thought. It emerges in the Homeric poems, where the psuchē is a breath-like stuff that animates the human being until it departs at death for the underworld, leaving the corpse (sōma or nekros) behind. In the Odyssey these souls are found lurking wraith-like in the underworld until they are revitalised by a sacrifice of blood which gives them a temporary power to think and speak again. Among Pythagoreans and others, the soul lives imprisoned in the body until it is liberated at death, only to be reincarnated for a new life in a new body in accordance with its merits. Plato embraces this theory in several of his dialogues, but even though the soul is a relatively autonomous substance it is nevertheless deeply affected by the conditions of the body it inhabits during life and the choices this embodied soul makes. Other early Greek thinkers regarded the soul as little more than the life force animating a body, a special kind of material stuff that accounts for the functions of a living animal but then disperses at death. Democritean atomism embraced this notion of soul, which was also common in the medical tradition.

Much has been written about Epicurus’ psychology. However, despite the enduring popularity of the theme, to the best of my knowledge no contribution has yet specifically been devoted to the reception of Epicurus’ psychology within the Epicurean tradition outside of Lucretius. The present essay therefore begins with some paragraphs of Epicurus’ Letter to Herodotus devoted to the soul, in order to ascertain how Epicurus’ psychology was represented by certain later Epicureans, most notably Demetrius Lacon (second to first century bc) and Diogenes of Oinoanda (second century ad), who lived not just in different ages but in very different places (the former, who never became scholarch, lived between Miletus and the mother school of Athens; the latter, between Oinoanda and Rhodes). In particular, I will set out to determine what the Epicureans made of the so-called bipartition between a rational and a non-rational part of the soul. While this theory is nowhere to be found in the Letter to Herodotus, it is espoused by Lucretius through the distinction between animus (the rational part) and anima (the non-rational part). In order to present as comprehensive a picture of the context as possible, it is best to start with Epicurus, and in particular with a challenging passage in §§ 63–4 of the Letter to Herodotus.

Although Aristotle’s thought became a byword in the early modern period for a rigid and inflexible system impervious to empirical evidence, it seems to have been quite otherwise in the practice of Aristotle’s own school. In reconstructing the psychological theory of the third head of the Lyceum, Strato of Lampsacus, I argue that we can best understand his departures from Aristotelian doctrine by looking to new medical theories in the Hellenistic period, which had implications for our philosophical understanding of the soul’s functioning. Aristotle, who was interested in the natural processes underlying even the most abstract aspects of human functioning, had lampooned the notion that the soul might exist apart from the body: his psychology posited an intimate connection between form and function, and was informed by empirical studies of living organisms. Strato was known even in antiquity both for a revisionist attitude and his focus on natural philosophy. It would thus be unsurprising for him to be interested in new medical research.