The present volume, a mighty work, is concerned with a central issue of Plotinus’ epistemology, namely, the problem of the precise nature of true knowledge, or knowledge in the strong sense, which is, for Plotinus, inevitably self-knowledge. In addressing this subject, Kühn adopts in various ways a novel and stimulating approach. First of all, he wishes to set Plotinus in perspective, by presenting his equating of objective certainty and self-knowledge as an attempt to counter the sceptical challenge to Stoic claims of certainty, as presented in particular (in surviving works) by Sextus Empiricus (specifically, at AM 7. 310-12). The argument goes somewhat as follows: “The intellect as a whole cannot know itself; for either one part of it is the knowing (subjective) aspect, and another the known (objective) aspect, which makes the knowing aspect distinct from the known aspect; or all of it knows all of it, and then the knowing aspect will be all, and the known aspect nothing. But whichever alternative one chooses, the concept of self-intellection is incoherent.” This argument is directed by Sextus against the Dogmatic (primarily Stoic) doctrine of cognitive certainty, which involves direct acquaintance with objects of knowledge, and would be a characteristic, not only of the human sage, but of the divine Intellect, which would primarily know itself.
Whether or not Plotinus knew Sextus’ work in particular (not impossible, but not as certain as Kühn seems to imply), he certainly knew this sceptical argument, and it plainly bothered him a good deal. It is the occasion for his detailed deliberations in Ennead 5. 3, and it is on that tractate, and specifically on chapter 5 of it, that Kühn’s large monograph is focused.
He begins with an introductory chapter, on ‘Themes and Method’, setting out his thesis, that Plotinus’ theory of self-knowledge has never before been looked at as a response to this sceptical argument, and therefore as an attempt to vindicate the concept of certainty against specific sceptical challenges—a claim that, so far as I can see, is perfectly justified, and introduces an interesting new perspective to the topic.
The body of the work he divides into three large sections. In the first, subtitled ‘Expliquer la connaissance de soi par la division de l’intellect’, he presents a detailed exegesis of the first part of chapter 5 (ll. 1-17). The main theme of this is a very detailed analysis of Plotinus’ attempts to address the problem of the ‘division’ of the intellect implied in the concept of ‘self-knowledge’. The problem of course is that knowing requires an object of knowledge, and even if that knowledge is of the contents of one’s own mind, this inevitably involves some degree of division within the intellect, between whole and part, and between a knowing element and a known element.
Plotinus, it seems to me, is perfectly aware of these difficulties, and is presenting them in an aporetic manner in order to bring home to us the very distinctive and unfamiliar nature of Intellect and its mode of self-cognition. Kühn sets out laboriously to pick apart Plotinus’ arguments line by line, in a manner that is certainly monumentally learned and acute, but one that I find somewhat inapposite to what is going on here. He does, however, make one think about the problem, and usefully adduces two earlier passages, from VI 7, 41 and II 9, 1, where these problems are already adumbrated.
This procedure continues, over Part II (‘La pensée vrai s’identifie à son objet’), covering ll. 17-31 (pp. 109-198), and Part III (‘Justification et description de la connaissance de soi’), covering ll. 31-48 (pp. 199-311). In ll. 17-31, Plotinus turns to a consideration of what is required for ‘truth’ ( aletheia), and sees this as consisting in intellection’s grasping, not typoi of its objects, but the objects themselves, which must therefore be identical with the knowing subject. Once again, Kühn embarks on a line-by-line analysis of the text, identifying many problems, and subjecting the concept of the equivalence of self-knowledge with knowledge of the objects of intellection to a close scrutiny.
In Part III, Kühn turns to the last section of the chapter in his division, ll. 31-48, in which he sees Plotinus as proposing his own conception of what is involved in self-knowledge. Plotinus’ argument here is that even the intelligible object must itself possess intellection, as it must be an activity, not just a potentiality, and it cannot be devoid of life. Once again Kühn picks his way through every line of this argument, adducing certain other relevant texts along the way, first II 5 , 3: On Potentiality and Actuality, where there is a good discussion of actuality in the intelligible realm; then VI 6 , 6: On Numbers, where Plotinus expounds the position that in the intelligible realm knowledge is identical with its object; then VI 7 , 13 and 9; then VI 6, 1, VI 7, 16, and V I  7, all of which throw useful light on the argument of the current passage, that intellect, intellection and the intelligible must be identical.
In his final section, Kühn turns back to examine the concept of self-knowledge in thinkers prior to Plotinus, in order to place the argument presented in V 3, 5 in historical perspective. He begins with Aristotle in Met. XII 9, dealing with divine self-knowledge, and continues with Eudemian Ethics VII 12 and Nicomachean Ethics IX 9, on human self-knowledge—though Aristotle’s reflections on human self-knowledge, while most interesting, might not seem particularly relevant to Plotinus’ problem in V 3, 5. Nonetheless, Plotinus does wish self-knowledge to comprise not just ‘knowledge of knowledge’, as is the case with Aristotle’s Prime Mover, but also knowledge of objects of knowledge, which promote self-consciousness in Aristotle’s theory of human self-knowledge—though of course, in the case of the Plotinian Intellect, the objects (sc. the Forms) are internal to itself.
At any rate, Kühn passes on from Aristotle to consider Alexander of Apohrodisias, whose influence on Plotinus’ thinking is generally agreed to be considerable, and he teases out the implications of a number of developments propounded by Alexander on Aristotle’s positions, particularly in the De Intellectu. He then ends more or less where he began, with a short review of the Stoic position on self-consciousness and self-reference, and criticisms of that from the Academic Sceptics.
Never, I think, in the history of Plotinian scholarship has such extensive attention been paid to a passage of this size. I calculate that there is an average of ten pages in Kühn’s text for every line of the selected chapter of V 3. However, this is a truly impressive achievement, and serves admirably to highlight Plotinus’ contribution to epistemology, and to place it in the context of philosophical disputes about epistemic certainty and the nature of self-knowledge, going back to Aristotle, the Stoics and the Sceptical Academy.