Book 4 of Lucretius’ de rerum natura (DRN) contains the most complete Epicurean account of perception and thought to survive from antiquity. In the course of the book’s detailed discussion of psychology, Lucretius responds to a variety of philosophical challenges to his physiological account: the nature of the relation between external objects and perception, the cause of mental visions, the difference between wakefulness and sleep, and the selectivity of attention. For this last topic he outlines a complex physiological process whereby either the mind or a sense organ (1) voluntarily, or actively, selects an image, or (2) involuntarily, or passively, is absorbed in a particular train of images. Lucretius’ account of attention (marked by expressions such as ‘se parare et contendere’), its varieties and their effects, is the subject of this dissertation.

My primary aim is to extract from the DRN a framework for understanding how and under what circumstances attention structures various types of intellectual and perceptual experience. The ‘how’ pertains to the physiological mechanism of attention. I show that Lucretius has at his disposal sufficient resources to account for the selectivity of attention entirely in terms of physical contact. The ‘under what circumstances’ turns on the distinction between voluntary and involuntary attention, a distinction which, I argue, Lucretius applies to both intellectual and perceptual attention. Not only does this distinction, hitherto unnoticed in the literature, unify Lucretius’ treatment of attention in Book 4 (4.794-817), it also illuminates a major philosophical problem for materialist psychology by explaining the manner in which intentional states (e.g., desire) that originate in the mind, motivate and guide the activities of the sense organs. Accounting for such a process puts a strain on the already limited resources of ancient atomism. To make matters even more difficult, any solution offered by an interpreter must be consistent with the demands of Epicurean epistemology. On this point, the question concerns the epistemic status of attention. Can the mind, by way of its desires, have a role in shaping the content of perceptual experience without impugning the claim that perceptions are veridical? I argue that Lucretius has sufficient resources in his physics to respond positively to this challenge: the use of perceptual attention, even when it is voluntary, does not introduce manipulation or interpretation into the perceptual process. It is, therefore, truth-preserving. On Lucretius’ account, voluntary perceptual attention is best understood as a genuine cognitive capacity (its mechanism involves the mind transmitting an atomic motion to the relevant sense organ), but the mind’s involvement in the attentive process does not prompt the perceiver to form an opinion about incoming images from the environment. Thus, Lucretius’ understanding of attention, once properly qualified, offers a corrective to a long-standing assumption that mind can have no meaningful role in the Epicurean account of perception, if perceptions are to be a reliable foundation for knowledge. On the contrary, I defend an alternative thesis that a perceiver’s desires and interests—past and present—affect the content of perceptual experience by determining what that perceiver notices.

In Part One, I extract from the DRN a taxonomy of forms of intellectual attention. I begin with the mind because Lucretius initially presents the mechanism of attention as a solution to why, given the abundance of images (simulacra, imagines) in the surrounding environment, we can think of one thing without also thinking of all things. In Part Two, at Lucretius’ invitation, I apply this taxonomy to Lucretius’ account of perceptual attention. In conclusion, I address the connection between Lucretius’ understanding of attention and Epicurus’ notion of epibolē, a much-vexed term, the meaning and significance of which is hotly debated in the literature.