Research

My research focuses on classical Greek and Hellenistic theories of rationality. More specifically, I investigate ancient debate over the rationality of sense-perception. To what extent does, e.g., seeing a cup on the table call upon distinctly rational cognitive resources, such as the ability to use language or apply concepts? What kind of information does sense-perception convey, and how is this information related to the contents of our beliefs? Does expertise affect the qualitative character of perceptual experience? Can we literally perceive ethical properties, such as the property of being courageous or being good? Are there any perceptual experiences which are guaranteed to be true?

The main strand of my research reconstructs the ancient Stoic answers to these questions. However, I also write about Platonic, Platonist, Aristotelian, and Epicurean accounts of the relationship between perception and reason. Below you will find summaries of some papers that I am currently working on.

In “Appearance and Assertion in Plato and Aristotle”, I explore a disagreement between Plato and Aristotle concerning the role which reason plays in generating our ‘perceptual appearances’ (phantasiai). According to the view we find in Plato’s late dialogues, to undergo a perceptual appearance requires the mind to make an assertion (apophasis) concerning the relationship between the perceptible objects in one’s surroundings. Humble as this psychological achievement may sound, Plato will nevertheless insist that it requires the mind to call upon the most advanced resources at its disposal, i.e., the peculiarly rational power to discern how this perceptible object is similar to, or different from, others like it. While many scholars share this interpretation, they support it by appealing to passages mainly from one dialogue, the Theaetetus. My approach, however, emphasizes a different set of Platonic texts — primarily the Sophist and Cratylus, which have received far less attention in comparison — in which Plato sketches a demanding theory of the psychological preconditions for making any assertion. I suggest that by focusing on Plato’s claim that perceptual appearances involve assertion, we can better understand not only his own motivations for identifying perceptual appearance as an opinion (doxa) of a certain kind, but also Aristotle’s criticism of this identification, which he expounds at length in the De Anima. On my reading, what Aristotle is objecting to in Plato’s treatment of phantasia is his insistence that it involves an assertion of a kind which presupposes the activity of reason. But for Aristotle, “perceptual appearance is other than assertion” (De Anima 3.8, 432a10-12), and so is available to guide the behavior of animals lacking reason but engaging in perception.

In “Perception and Reason in Ancient Stoicism”, I argue that, for the Stoics, the perceptual experiences of adult humans are both cognitively penetrated and sententially structured: on this interpretation, (i) the phenomenological character of an adult’s perceptual experience is sensitive to the concepts she has formed, and (ii) the content of these experiences displays a structure exemplified by that of a sentence. In a departure from the consensus interpretation of the ‘rational appearance’ (phantasia logikê) — the Stoic term for the perceptual experiences undergone by adult humans — this paper breaks new ground by suggesting that the content of a rational appearance is exhausted by its sentential content: its content is thus exclusively sentential. I contend that by adopting this view, the Stoics can adequately defend their account of what beliefs are and how they are related to our perceptual states: if the content of perception has the same structure as that of belief, then it is unproblematic to identify beliefs as the acceptance of what a perceptual experience represents, and there will be little mystery in how the subject comes to hold beliefs on the basis of perception.

Besides furthering our understanding of the Stoics’ intriguing theory of cognition and perception, clarifying their account of the rational appearance also sheds light on their epistemology. Both in antiquity and the present day, the signal achievement of Stoic philosophy is often taken to be their defense of “cognitive” or “kataleptic” appearances (phantasiai katalêptikai). According to the Stoics, by forming a kataleptic appearance, and then assenting to it, we are assured to get things right: whatever the kataleptic appearance says about the external world reflects the way it actually is, and in accepting this appearance as true we thereby acquire knowledge. 

In “Creating a Mind Fit for Truth” — forthcoming in Ancient Philosophy — I argue that, by attending carefully to the process by which the human mind forms any rational appearance, whether kataleptic or not, we can make progress on a long-standing interpretative puzzle: how can a rational subject detect whether an occurrent appearance is kataleptic, and so worthy of her acceptance? My proposal is to interpret the Stoics as holding that a subject can train her mind to such an extent that she becomes expert in the circumstances which conduce to forming a kataleptic appearance — including, crucially, the condition of her own mind and senses. The subject will thereby possess an accurate guide to the reliability of a given appearance even when that appearance displays no obvious phenomenological defect like blurriness or focal distortion. In advancing this interpretation, I reject an influential characterization of the kataleptic appearance on which it is “self-evident”, in the sense that its epistemological credentials may be verified solely by consulting its phenomenological character.

In “Imprinting and Sealing in Stoic Epistemology”, I investigate the influence of Plato’s Theaetetus on the development of the Stoic doctrine of the kataleptic appearance. In characterizing our appearances as “imprints” in the mind, and the kataleptic appearance in particular as one that is “stamped and molded on the basis of the very thing that obtains” (DL VII.45-46), the early Stoics deploy a metaphor familiar to readers of the Theaetetus, which compares the human soul to a wax-tablet, capable of taking on “impressions” left by external objects of perception and storing them in memory (191a-196c). Here Plato goes on to sketch a view on which one’s perceptual opinion cannot be false in the case where one accurately matches a stored memory-imprint with its appropriate object of perception. In disagreement with other commentators, I argue that Stoic epistemology in large part retains these features of Plato’s model, insofar as the Stoics analyze the kataleptic appearance as one whose content cannot be false, in virtue of applying the concept appropriate for the external object that it represents.

An exciting aspect of my investigation into the Stoic theory of the rational mind is that it has furnished new tools to analyze the Stoic account of the psychology of creatures who lack reason. In “Cognition without Concepts: the Stoics on Non-Rational Animal Minds”, I consider the question of how the appearances of non-rational animals represent external objects, given the limitations the Stoics impose on the type of information these animals can receive. Since the Stoics allow concepts and language only in rational animals, I argue that non-rational appearances must convey information that is not presented in conceptual or linguistically structured terms. I then show that this kind of nonconceptual and non-linguistic content, as the Stoics understand it, is robust enough to ground the cognitive achievements they ascribe to animals. In particular, I argue that nonconceptual and non-linguistic content can be complex, in the sense that it allows an animal to see an external object as an instance of a kind. 

The limitations of non-rational cognition is also the central theme of my work on Epicurean epistemology. Diametrically opposed to the Stoic view, the Epicureans characterize every act of sense-perception as both (i) non-rational and (ii) infallible, somehow inferring (ii) on the basis of (i). In “Epicurus on Perception and Prolêpsis, I investigate this inference, offering a reconstruction of the Epicurean commitment to the non-rationality of perception, which, in conjunction with other Epicurean views, arguably secures its infallibility.

Like the Hellenistic philosophers themselves, I am interested in how psychology informs ethics.  In “Diseases of the Soul: Vicious Dispositions and Rational Assent”, I draw on my past work on the Stoic theory of cognition and perception to illuminate these philosophers’ notorious claim that the virtuous human life is free of emotion. As is widely recognized, the Stoics analyze an emotion as the acceptance of a certain kind of appearance, one which vividly depicts some present or future state of affairs as necessarily beneficial or harmful to the subject. My aim is to situate the Stoic theory of emotion within their more general theory of the rational appearance. Because of differences in their upbringing, rational subjects will employ different concepts in forming appearances of the same object. The Stoics call these patterns of concept application ‘dispositions’ (diatheseis) of the soul, and claim that one can learn to withhold assent on appearances formed this way if one receives the right sort of training. Emotional appearances, then, will display vivid phenomenology, but this vividness will be due to the dispositions involved in their generation and so potentially resisted with proper moral therapy. Looking at the Stoic theory from this perspective also promises to further our understanding of an intra-school debate over the nature of the emotions. I take up this theme in the paper I am currently developing, “Answering Posidonius’s Objections to the Chrysippean Theory of the Emotions”.

I am also interested in exploring the distinction between rational and non-rational cognition as it is developed by Plotinus, a Platonist philosopher writing in the third century CE. Despite a long-standing reputation for obscurity, Plotinus’s texts offer an innovative and sophisticated account of the distinctive aspects of the rational mind, albeit one which relies on metaphysical assumptions we may blanch at today. For Plotinus, as for any Platonist, there is a fundamental ontological difference between the world as revealed by one’s senses and the world of the intellect: the former is a poor imitation of the latter, where true reality is located. Given this view, Plotinus locates the human self not in the body, which occupies the sensible world, but rather in our capacities to access the world of the intellect. In fact, on his view, it is these capacities which distinguish human beings from all other animals. Now, if one retains these metaphysical commitments, a puzzle arises for one’s account of sense-perception: what entities do the activities of sense-perception put us in touch with, and how are these related to the ‘Forms’ which constitute the world of the intellect? Do the perceptual experiences of humans differ from those of non-rational animals, in virtue of our unique capacity to access true reality? In “Plotinus on the Soul-Image’s Cognition of Perceptible Form”, I hope to situate Plotinus’s answers to these questions within a larger context of ancient inquiry into the relationship between perception and reason and the structure of the content of our perceptual experience.