Chapter 14 - Platonist Notions and Forms

Summary

In ‘Platonist Notions and Forms’, Mauro Bonazzi explores an aspect of the Platonists’ engagement with Stoic epistemology, namely the Platonists’ appropriation of the Stoic ennoiai, conceptions or notions, to show that Plato’s doctrine can provide a satisfactory answer to the problem of the foundation of knowledge, which Stoicism has proved unable to solve. The Stoic ennoiai, (conceptions) or phusikai ennoiai (natural conceptions) are notions naturally arising in the human mind and constituting the basic elements of human reason. They are ‘natural’ in the sense that humans are naturally disposed to acquire them, and they are koinai (common) in the sense that all humans have them or are disposed to have them. They are also invariably true and therefore can serve as criteria in order to increase knowledge, promote scientific understanding and contribute to the good life. It is these ennoiai that the Platonists integrate in their own reinvention of Plato’s epistemology and employ in their polemics against their principal rivals.

1 Introduction

Platonism consists in the interpretation of Plato’s dialogues based on the assumption that his philosophy can be organised into a coherent system. This is what ancient Platonists would have replied, if asked about their allegiance. But Platonism is not only an exegetical enterprise, as many scholars have now explained. The polemical dimension was equally important. At the time of its revival, in the early imperial centuries, Platonism was also the result of an engagement with the other schools, most notably the Hellenistic ones.¹ Indeed, the need for this engagement was somehow stimulated by the historical and philosophical context in which Platonism had developed after the sceptical phase of Arcesilaus and Carneades’ Academy. For centuries, the Hellenistic centuries, different schools – Stoics, Academics, and Epicureans – had debated with one another, which produced a common language and a unification of the philosophical agenda and the problems to be discussed. In their effort to gain visibility, the Platonists were forced to take part in these debates; and in order to vindicate Plato’s superiority, they also had to prove that his thought was capable of solving the problems which these schools had been unsuccessfully investigating for centuries. From a concrete perspective, this engagement led them to use a vocabulary and discuss issues which were not explicitly present as such in the dialogues or epistles. In most cases, the Platonists adopted an appropriation strategy by attributing to Plato notions and doctrines which had been central in Hellenistic debates. The new solutions they offered to the old problems were often interesting but entailed certain risks, as I will argue by focusing on their epistemological theories.

Given the importance of this debate, it was therefore predictable that the Platonists would also take part in it by appropriating some Hellenistic (most notably Stoic) notions and doctrines and attributing them to Plato, as if they originally came from his dialogues. To be sure, this might strike us as surprising: it seems that there is very little in common between Hellenistic philosophies (particularly Stoicism) and Platonism. How is it possible to argue for a continuity between the Stoic attempt to ground the very possibility of knowledge in sensation and Platonist metaphysics, with its constant anti-empirical polemics? Quite to the contrary, I shall argue that not only were the Platonists interested in the epistemological problem of the foundation of knowledge, but their position resulted from an appropriation of Stoic doctrine.

The starting point for our investigation will be a term, ennoia (notion, conception), which will help us to understand that the situation is more complex than it is normally taken to be. Admittedly, at first sight the differences between the Stoics’ kataleptic impressions and the Platonists’ anti-empiricism might appear too strong to be reconciled. But the Stoics, along with the phantasiai katalēptikai, also emphasised the importance of another criterion of knowledge, that is, ennoiai, notions or conceptions.² Most poignantly, this term also plays an important role in the Platonist tradition, and this is a parallel that is worth investigating.³

2 Stoic and Platonist ennoiai

The Stoic doctrine of ennoiai is a notoriously difficult one, and it is difficult to account for all its technicalities. Yet what we can glean from the sources suffices to show its role in the Stoic epistemological system.⁴ Briefly put, ennoiai are those conceptions which come to constitute our mind (literally, reason is the collection of our conceptions: ‘Reason is a collection of certain conceptions and preconceptions’)⁵ as the result of repeated sense-experience.⁶ According to the Stoics these ennoiai naturally arise in the minds of all human beings, and for this reason, since they come about spontaneously (that is, without effort and without any specific education or reasoning), they are called ‘natural’ (physikai); insofar as they are natural, they are also taken to be true. And they are also called ‘common’ (koinai) because they belong to all human beings. Since they are true, they have the status of cognitions and they can be used as principles from which to derive further truths⁷ or as yardsticks against which philosophical views may be tested.⁸ Clearly, all that is correctly deduced from these cognitions, will itself have the status of a cognition. In this way we obtain a whole range of cognitions, and by correctly developing them into definitions,⁹ we will achieve wisdom, which is the condition for a happy life.¹⁰ In short, conceptions are ‘constitutive of reason and the basis from which philosophical inquiry, and hence ultimately wisdom or perfected reason, sprang’.¹¹ This is why, as the Stoics say, they are the criterion of truth. Their epistemological importance is clear.

The Platonists were aware of the Stoic use of the term and its function within the Stoic system, as an important text from Plutarch shows.¹² Remarkably, however, they also used it in their interpretation of Plato, implicitly suggesting that it is perfectly compatible with the philosophy of the dialogues. The term is a recurrent one in Platonist texts, even in later periods, from Plotinus to Byzantine Platonism.¹³ Clearly, this parallel is not accidental; it rather implies an attempt on the Platonists’ part to appropriate the term – and more, as will become clear.

Among the surviving sources, the anonymous commentary on the Theaetetus is the best attested testimony and probably the most useful evidence to reconstruct the Platonist strategy.¹⁴ In the commentary ennoia occurs several times, always in a topical position, when the author is explaining Plato’s theory of knowledge. Ennoiai are the starting point in the process of knowledge, and they lead to proper knowledge when adequately ‘articulated’ into definitions:

For the natural conceptions are in need of articulation (hai gar phusikai ennoia deontai diarthrōseōs). Before this, people apprehend things, insofar as they have traces of the natural conceptions; but they do not apprehend them clearly.

(Anon., in Theaet. 46.43–9; trans. Boys-Stones)

But definitions are not adopted as greetings or as being more concise than names, but are used to unfold common conceptions (alla pros to anaplōsai tas koinas ennoiai). This does not happen without getting each genus and the differentiae.

(Anon., in Theaet. 23.1–12; trans. Boys-Stones)

Conceptions are the starting point, and the task is to develop and clarify them; then, once they have been articulated, they will lead to formal definitions which are the basis for scientific knowledge, or epistēmē. The further systematization of these pieces of epistēmē – which the anonymous commentator calls episteme haplē (simple knowledge) – into ‘composite knowledge’ (epistēmē sustematikē) will finally bring about ‘a systematic understanding of the world’:¹⁵

The discussion is not about composite knowledge (what some people call ‘systematic’ knowledge) but about simple knowledge such as the cognition of individual theorems which go to make up geometry and music. These individual items of cognition go to make up one composite body of knowledge (what is simple is prior to what is composite). He defined this [sc. ‘simple’ knowledge] in the Meno as ‘right opinion bound by an explanation of the reasoning’; Aristotle defined it as ‘supposition with proof’; Zeno as a ‘disposition in the receipt of impressions which is not subject to modification by argument [ …]

(Anon., in Theaet. 15.3–30; trans. Boys-Stones)

As this last quotation clearly shows, the anonymous commentator is willing to reconcile Plato and the Stoics (and Aristotle), as if their theories were the same. Indeed, this theory very much resonates with Stoic echoes. For the commentator, however, the reconstruction of this process is perfectly Platonic, as the following reference to anamnēsis shows:

But when he was teaching, he prepared his students to talk about things themselves, unfolding and articulating their natural conceptions. And this way of doing things follows from the doctrine that so-called acts of ‘learning’ are in fact acts of remembering, and that the soul of every man has seen what exists and does not need learning to be placed in it, but needs reminding.¹⁶

(Anon., in Theaet 47.37–48.7; trans. Boys-Stones)

As this passage makes clear, the Stoic theory is inserted in a broader Platonic context, with ennoiai somehow being linked to the Forms and reminiscence. The process of learning, of articulating ennoiai into proper definitions, corresponds to reminiscence and thus implies the existence of Forms. Unfortunately, only a small section of this long commentary has been preserved, so it is difficult to reconstruct the author’s theory in its entirety. Interestingly, however, another important testimony, Alcinous’ Didaskalikos, presents many parallels with the anonymous commentary and contributes to a better understanding of the Platonist view. As a matter of fact, Alcinous uses ennoia like the anonymous commentator.¹⁷ Besides, he also explicitly explains the relation between ennoiai and Forms, which is only implicit in the commentary. Ennoiai are what remains of the pre-natal vision of the Forms:

Intellection is the activity of the intellect as it contemplates the primary objects of intellection. There seem to be two forms of this, the one prior to the soul’s coming to be in this body, when it is contemplating by itself the objects of intellection, the other after it has been installed in this body. Of these, the former, that which existed before the soul came to be in the body, is called intellection in the strict sense, while, once it has come to be in the body, what was then called intellection is now called ‘natural conception’ (phusikē ennoia), being, as it were, an intellection stored up in the soul.

(Alc., Did. 150.20–32; trans. J. Dillon)

The end of the investigation will of course lead once again to Forms, wisdom and happiness (homōisis):

Contemplation, then, is the activity of the intellect when intellegizing the intelligibles […]. The soul engaged in contemplation of the divine and the thoughts of the divine is said to be in a good state, and this state is called ‘wisdom’, which may be asserted to be no other than likeness to the divine.¹⁸

(Alc., Did. 152.30–153.9; trans. Dillon)

The association between Forms and ennoiai clearly introduces important differences between the two schools. As is known, the Stoics vehemently denied the existence of Plato’s Forms. For the Platonists, by contrast, Forms play a crucial role as the foundation for ennoiai and the conclusion, and confirmation, of the whole process. Natural conceptions are now ‘grounded in our incorrigible prenatal experience of Forms’.¹⁹ Ennoiai are somehow what remains of the contemplation of the Forms and when they are adequately developed, or articulated, they lead to the contemplation of Forms, and hence to proper knowledge. For the Platonists, the Stoics were basically endorsing an empiricist epistemology. The Platonists then reshaped the same theory as a metaphysically innatist one. Besides, this reintroduction of Forms produces a radical split between opinion (doxa) and knowledge (epistēmē). While according to the Stoics there only exists a single reality (made up of particular individuals: LS 1987: 30), which can be known either with certainty – this being epistēmē – or without certainty – this being doxa – according to the Platonists there are two realities, the intelligible world of Ideas and of real knowledge and the sensible world of opinion. Hence, although the theory is structurally the same, it is substantially different. The Platonists insert the Stoic tenets in a new metaphysical context, originally absent. The problem, therefore, is how to interpret this interplay of doctrines. What does it mean that a Stoic term is used by the Platonists in order to account for their own epistemological views?

2.1 The Metaphysical Foundation of ennoiai

In the past, several scholars explained these parallels as if it were simply a matter of a shared language, the specific terminology of which gradually lost its original philosophical connotation and became common to all philosophers in an epoch of eclecticism. By contrast, other scholars have remarked that the term was already present in Plato’s dialogues,²⁰ thereby concluding that the Platonists were simply following Plato without paying proper attention to the Stoic theories.²¹ Neither of the two interpretations is convincing. With regard to the former claim, it is probably right to say that there was a common jargon at the time, but this does not imply that the adoption of any given term was always or necessarily neutral. As Tony Long very aptly remarked – and as this paper hopefully shows – ‘[w]hat came to be shared […] was not just words or concepts, but something we might call professionalism or expertise’.²² With regard to the latter claim, the occurrence of the term in the dialogues, important as it is, does not suffice to account for their importance in Platonist texts. In Plato ennoia does not have the philosophically loaded meaning that it has in Stoicism and Middle Platonism.²³ The Platonists could surely exploit the occurrences in the dialogues in order to make a claim for Platonic priority, but their initial interest in the term was due to the fact that they were reacting against the Stoic and Hellenistic uses of it. As it turns out, they were aware of the Stoic use of the term but nevertheless chose to adopt it; moreover, they used it in explicit connection with the doctrine of Forms. All this suggests a conscious engagement on their part, and therefore another explanation is called for.

A more convincing explanation emerges when we take into account the reasons which justify the innovations introduced by the Platonists. Such innovations are clearly derived from the dialogues and aimed at improving the Stoic doctrine. The problem, therefore, is to understand in what respect such innovations, according to the Platonists, improve the Stoic doctrine: in other words, we must try to determine what the limits of the Stoic theory are that the Platonist innovations are meant to solve. The answer is clear. The problem does not reside in ennoiai themselves or in the Stoic theory as a whole (which the Platonists, as we have seen, were willing to use); the problem is rather that the Stoics were unable to adequately account for the importance of ennoiai, that is, for their criterial role. Clearly, if ennoiai are criterial, we must be sure that they are true and capable of truly describing their objects; we must justify placing so much confidence in them.²⁴ Now, from a Platonist point of view, the problem is that the Stoics were unable to correctly account for the criterial role of the ennoiai, since they explained how ennoiai come about in a fallacious way. For the Stoics, sense-perception ‘is the foundation of all our conceptions’.²⁵ Now, the Platonists are convinced that any attempt to empirically account for the formation of ennoiai is bound to fail. In other words, the problem is not so much the doctrine itself, as the grounds on which it rests. Broadly speaking, what is at stake here is what we might call ‘the naturalistic assumption’. For the Stoics, the very fact that our mind is by nature constructed in such a way as to naturally form notions constitutes sufficient proof of their reliability.²⁶ For the Platonists such an assumption is not correct at all. Raw ‘empirical experiences do not have the regularity or consistency to carve out clear conceptual divisions of the mind’.²⁷ Indeed, the Platonists argue, against the Stoics, that nothing reliable may be produced by sensory experience alone; (a) for matter, that is, the sensible world, is unstable and (b) human senses are notoriously weak:

In fact, we find ourselves moved by things in different ways, and not able to say anything certain about anything, because what appears to us is not fixed, but changes in many ways into many forms. And since impression lacks secure foundation, judgment of it lacks sure foundation as well

(Philo, On Drunkeness 169–71; trans. Boys-Stones)²⁸

This critique is certainly too radical, and it does not take into account the subtleties of the Stoic doctrines; however, it does raise interesting problems. What is at stake is the cognitive value of these ennoiai and what it means to say that they are reliable: ennoiai might be taken to be reliable in either a broad sense or in a stricter and more technical sense. In the first, broader sense ennoiai are reliable because they are a common-sense grasp of universal conceptions; in the second and more technical sense, they are reliable because they are a deeper grasp of the real essences (let us think, for instance, of Locke’s distinction between ‘nominal’ and ‘real essences’).²⁹ Now, if the Platonists object to the Stoics that it is not true that we naturally form reliable ennoiai according to the first connotation (i.e. ennoiai which enable us to get in touch with reality), then it seems as though they are upholding a paradoxical and rather unsatisfactory thesis: for the Stoics seem to be right in claiming that we naturally develop notions which help us to live.³⁰

The Stoic doctrine, however, requires much more:³¹ not only generically reliable conceptions but conceptions which truly describe the essential features of an object. As already mentioned, ennoiai are the basis for epistēmē – that is, scientific knowledge – and in order to serve as a trustworthy criterion for epistēmē, it is not enough for ennoiai to give us a generically reliable description of an object: they must also provide us with the essence of that object.

We might accept that we naturally produce ordinary notions; but in order to prove that ennoiai also give us the essence of the object, something more, such as a proper argument, seems necessary in addition to the simple naturalistic assumption. According to the Platonists, not only do the Stoics not offer any further argument, but their empiricist thesis itself precludes the very possibility of any further argument. The Platonists, in other words, do not attack the possibility of empirical concept formation, but rather the idea that empiricism can provide stable foundations for epistemic claims about the world.³²

With regard to this last point, a passage from Alcinous proves highly interesting:

That learning is remembering we may infer as follows. Learning cannot arise in any other way than by remembering what was formerly known. If we had in fact to start from particulars in forming our conception of common qualities (enenoousmen tas koinotētas),³³ how could we ever traverse the infinite series of particulars, or alternatively how could we form such a conception on the basis of a small number (for we could be deceived, as for instance if we came to the conclusion that only that which breathed was an animal); or how could concepts function as principles?³⁴ So we derive our thoughts through recollection, on the basis of small sparks, under the stimulus of certain particular impressions remembering what we knew long ago, but suffered forgetfulness of at the time of our embodiment (ἢ πῶς ἂν τὸ ἀρχικὸν εἶεν αἱ ἔννοιαι; ἀναμνηστικῶς οὖν νοοῦμεν ἀπὸ μικρῶν αἰθυγμάτων, ἀπό τινων κατὰ μέρος ὑποπεσόντων ἀναμιμνησκόμενοι τῶν πάλαι ἐγνωσμένων, ὧν λήθην ἐλάβομεν ἐνσωματωθέντες; Alc., Did. 177.45–178.10; trans. Dillon, slightly mod.).

Alcinous’ argument is clear. By using induction one can attain the notion (enenooumen, see note) of animals as breathing beings. Yet, clearly, this notion does not hold true: for some animals exist which do not breathe.³⁵ The issue at stake here is that induction and, more generally, any other method grounded in sense-experience does not give us any means to distinguish such an incorrect notion from a true one; hence, empirically derived notions cannot meet the standards of real scientific knowledge (epistēmē).³⁶

Alcinous’ example therefore clarifies what the real issue at stake is. The problem is the transformation of these vague ennoiai into scientific definitions (or into a complete grasp of the object, as Cic., Acad. Pr. 21 has it). This was not a problem for the Epicureans, since they were quite happy with ordinary notions and denied any value to definitional inquiry (see the above-quoted text from Anon., in Theaet. 22.39–23.12). But this was precisely what Stoics and Platonists were after: they were interested in essences, definitions and so on. And it is unclear how the Stoics could adequately argue in favour of their position. We may admit that we naturally produce ordinary notions, but that these ordinary notions contain essences is a claim that should be proved; and if it is not proved, it is legitimate to doubt the correctness of the conclusions. As the anonymous commentator puts it: ‘But since the Stoics establish this when it does not need proof…’ (Anon., in Theaet. 70.20–26).³⁷ In other words, the Stoics pretend to offer a demonstrative explanation of empirical evidence with the aim of attaining knowledge. This is an impossible task for the Platonists. The strategic importance of recollection and of Forms becomes clear.

If ennoiai are the criterion, and if they are to effectively serve as a criterion, we must be certain that they are true. The Stoic empiricist explanation fails to establish the trustworthiness of ennoiai, but luckily the Platonists have a solution: they have developed a theory that may account for the formation of ennoiai in a non-empiricist way by making ennoiai depend on the prenatal view of Ideas and by claiming that ennoiai are reactivated by the process of recollection. This is also why we can rely on them for scientific knowledge: once correctly articulated into definitions, they will lead us to the Forms. Without Forms, there is no justification for confidence in empirical concepts. In Platonist thought, this correspondence between the articulated ennoia and the Form becomes the foundation for epistēmē.³⁸

It is worth pointing out that this last claim about the combination of ennoia and Form as the foundation of knowledge implies a further critique of the Stoic doctrine, a critique directed against the conclusion of the epistemic process. As it turns out, the doctrine of ennoiai raises a further difficulty: how can we be certain of our attainment of epistēmē? As Plutarch remarks in fr. 215, it is unclear in what sense the articulation of an ennoia (i.e., of a notion which is not entirely clear yet) may provide assurance as to the fact that we have obtained the real essence of the given object.³⁹ The famous debate between Stoics and Epicureans on the nature of God is quite revealing; but even more telling, perhaps, is the problem of getting a clear notion of what is good, which cannot rest on any empirical foundation given the virtual non-existence of the wise person: ‘there is no way of apprehending the Good from some perceptible similarity’.⁴⁰ By contrast, the Platonist theory, insofar as it leads us to the vision of the Ideas, is regarded as solving this difficulty.⁴¹

In sum, the Stoics were unable to justify the criterial value of ennoiai and to explain how one can be sure that one has obtained knowledge. The importance of ennoiai was never questioned, but for the Platonists it was clear that the Stoics were unable to account for their importance. The Platonists’ strategy is therefore clear: they did not reject Stoic doctrine (in this case, the theory of ennoiai as a criterion for epistēmē) nor did they reject the scope of Stoic theory (the commitment to the view that knowledge is possible): both the theory and the commitment to the possibility of knowledge were accepted. The Platonists objected that the Stoics could not properly account for their theory, since they mistakenly persisted in defending an empiricist account. The Stoic theory was in itself correct, but it was inadequately grounded. The Platonist reshaping of this theory offered an explicit solution by providing a metaphysical foundation for it. Plato’s theory was clearly superior: it included everything that made the Stoic theory attractive and, in addition, provided a way of overcoming its limitations.⁴²

2.2 Is Knowledge of Forms Possible?

So far so good, for the Platonists. The task of combining the exegesis of Plato’s works and anti-Hellenistic polemics, however, was not entirely unproblematic. The Platonists had good arguments against the empiricist foundation of ennoiai. But Plato’s works also raised unexpected problems when the Platonists had to provide their own metaphysical foundation to the theory.

As it turns out, the Platonist anti-Stoic argument works on the assumption, shared by both Platonists and Stoics, that knowledge is possible. Their argument can thus be constructed in the form of a disjunction: either a or b; but not a (empiricism), therefore b (Platonism). If knowledge exists, it must be grounded either in the senses or in the Forms. Now, since it cannot be grounded in the senses, it is necessarily grounded in the Forms. But what if the possibility of knowledge were not taken for granted? This is also an option, which frustrates the disjunctive opposition between sense-perception and Forms. Translated into the terms used in the Platonists’ debates, this question leads to the problem of Forms. Forms are regarded as the foundation for knowledge. What if they cannot be known? This was the unexpected problem Platonists had to face when interpreting Plato’s works. For in the dialogues, it is far from clear how the Forms can be known, if at all. Like today, in the early centuries of the Imperial age Platonists intensely considered this problem, apparently without being aware of the consequences that it had for their appropriation of the Stoic doctrine.

Remarkably, very few Middle Platonist texts explicitly claim that we can acquire knowledge of Forms in our embodied life; besides, when they do it, they do it in very specific contexts. The three most eloquent testimonies, from Plutarch, Celsus and Numenius, have been collected by George Boys-Stones in his recent sourcebook. Celsus’ text and Numenius’ are clearly interlocutory or polemical (the former is addressed against Christians, the latter against empiricism), and contain generic allusions to some very famous passages from Plato’s works (the Seventh Letter and the Idea of the Good respectively).⁴³ Epistemologically, therefore, they are not very informative. As for Plutarch, he models his text on Diotima’s speech in the Symposium and this seems to suggest that some kind of intuitive knowledge of the Forms is possible.⁴⁴ Plutarch himself, however, offers a perfect example of the ambiguities and fluctuations of these Platonists: not only is he often reticent when talking about Forms, but he even argues that they cannot be properly known, insofar as this would equate us with God. As the prologue of De Iside et Osiride explains, proper and exhaustive knowledge of the Forms is distinctive of God; it cannot therefore be attributed to us.

All blessings, Clea, should be sought of the gods by the intelligent, and especially pray that in our search we may receive direct from them an understanding of their own nature, as far as that is possible to men; for nothing greater is attainable by man, and nothing nobler can be granted by God, than truth. […]. For this reason the longing for truth, particularly the truth about the gods, is a yearning after divinity, since it involves in its training and intellectual pursuit an acquirement of sacred lore which constitutes a holier task than all ceremonial purification and temple service, a task which is supremely welcome to this goddess whom you worship as one who is exceptionally wise and devoted to wisdom.

(De Iside et Osiride 351C-F; trans. Griffiths)

This text is extremely important, because it explains the problem at stake and the inevitable epistemological consequences of the new interpretation of Plato which became dominant in the first centuries of the Imperial age. The theological reshaping of his philosophy inevitably forced Platonists to adopt much caution (eulabeia being a key term in Plutarch’s epistemology)⁴⁵ when dealing with this problem. Plutarch offers a clear example, but similar fluctuations can be found in other important authors, such as Philo of Alexandria and even Alcinous.⁴⁶ The belief that a proper (and pure) grasp of the transcendent Ideas is not attainable by human beings in their corporeal lives is a widely shared belief among Platonists, supported both by theological reasons (the emphasis of the theological dimension in Plato’s thought) and exegetical reasons (several passages of the dialogues explicitly stating that Ideas are not known in our lifetime).

Surprisingly, the Platonists do not seem to be aware of the consequences of this position, but the consequences become quite clear once this thesis is viewed in relation to their appropriation of the Stoic theory. Indeed, it may be argued that the Platonist thesis reproduces the problems of the Stoic one on a different level. Like the Stoic thesis, it does not offer any convincing answer to the sceptical challenge, which played such a prominent role in Hellenistic debates. The problem, during the Hellenistic centuries, was to explain not so much how knowledge works, as that knowledge is possible. This was the purpose of the Stoic thesis. As already mentioned, the Platonist appropriation of the Stoic theory could be used as an anti-empiricist argument, to expose the limits of the Stoic theory. But in itself such a doctrine does not appear to be a sufficient explanation for the more radical question raised by the sceptics. How could it be, if Platonists affirmed that Forms, the ultimate criterion, were not the object of exact knowledge? The Stoics’ controversial problem was the ‘naturalistic assumption’; but, ultimately, the Platonist ‘metaphysical assumption’ was no less controversial. And scepticism seems to be the only viable conclusion. As Sextus Empiricus claims with an eloquent allusion to Plato’s Meno, one of the most important dialogues for these epistemological debates: in the absence of a proper foundation, there is no possibility of moving from opinion to knowledge (Sext. Emp. M. 8.331a–2a). It is unsurprising, therefore, that Plotinus, a stark opponent of any form of scepticism, accused Platonists of being crypto-sceptics and developed a completely different theory in order to escape all these problems. But whether his new theory was capable of solving all the difficulties his predecessors had been incapable of solving is something which needs to be discussed.⁴⁷