The Stoic theory of universals, as compared to Platonic and Aristotelian theories

By Tim Harding

The philosophical problem of universals has endured since ancient times, and can have metaphysical or epistemic connotations, depending upon the philosopher in question.  I intend to show in this essay that both Plato’s and the Stoics’ theories of universals were not only derived from, but were ‘in the grip’ of their epistemological and metaphysical philosophies respectively; and were thus vulnerable to methodological criticism.  I propose to first outline the three alternative theories of Plato, Aristotle and the Stoics; and then to suggest that Aristotle’s theory, whilst developed as a criticism of Plato’s theory, stands more robustly on its own merits.

According to the Oxford Companion to Philosophy, particulars are instances of universals, as a particular apple is an instance of the universal known as ‘apple’.  (An implication of a particular is that it can only be in one place at any one time, which presents a kind of paradox that will be discussed later in this essay).   Even the definition of the ‘problem of universals’ is somewhat disputed by philosophers, but the problem generally is about whether universals exist, and if so what is their nature and relationship to particulars (Honderich 1995: 646, 887).

Philosophers such as Plato and Aristotle who hold that universals exist are known as ‘realists’, although they have differences about the ontological relationships between universals and particulars, as discussed in this essay.  Those who deny the existence of universals are known as ‘nominalists’.  According to Long and Sedley (1987:181), the Stoics were a type of nominalist known as ‘conceptualists’, as I shall discuss later.

Plato’s theory of universals (although he does not actually use this term) stems from his theory of knowledge.  Indeed, it is difficult to separate Plato’s ontology from his epistemology (Copleston 1962: 142).  In his Socratic dialogue Timaeus, Plato draws a distinction between permanent knowledge gained by reason and temporary opinion gained from the senses.

That which is apprehended by intelligence and reason is always in the same state; but that which is conceived by opinion with the help of sensation and without reason, is always in a process of becoming and perishing and never really is (Plato Timaeus 28a).

According to Copleston (1962: 143-146), this argument is part of Plato’s challenge to Protagoras’ theory that knowledge is sense-perception.  Plato argues that sense-perception on its own is not knowledge.  Truth is derived from the mind’s reflection and judgement, rather than from bare sensations.  To give an example of what Plato means, we may have a bare sensation of two white surfaces, but in order to judge the similarity of the two sensations, the mind’s activity is required.

Plato argues that true knowledge must be infallible, unchanging and of what is real, rather than merely of what is perceived.  He thinks that the individual objects of sense-perception, or particulars, cannot meet the criteria for knowledge because they are always in a state of flux and indefinite in number (Copleston 1962: 149).  So what knowledge does meet Plato’s criteria?  The answer to this question leads us to the category of universals.  Copleston gives the example of the judgement ‘The Athenian Constitution is good’.  The Constitution itself is open to change, for better or worse, but what is stable in this judgement is the universal quality of goodness.  Hence, within Plato’s epistemological framework, true knowledge is knowledge of the universal rather than the particular (Copleston 1962: 150).

We now proceed from Plato’s epistemology to his ontology of universals and particulars.  In terms of his third criterion of true knowledge being what is real rather than perceived, the essence of Plato’s Forms is that each true universal concept corresponds to an objective reality (Copleston 1962: 151).  The universal is what is real, and particulars are copies or instances of the Form.  For example, particulars such as beautiful things are instances of the universal or Form of Beauty.

…nothing makes a thing beautiful but the presence and participation of beauty in whatever way or manner obtained; for as to the manner I am uncertain, but I stoutly contend that by beauty all beautiful things become beautiful (Plato Phaedo, 653).

Baltzly (2106: F5.2-6) puts the general structure of Plato’s argument this way:

What we understand when we understand what justice, beauty, or generally F-ness are, doesn’t ever change.

But the sensible F particulars that exhibit these features are always changing.

So there must be a non-sensible universal – the Form of F-ness – that we understand when we achieve episteme (true knowledge).

Plato’s explanation for where this knowledge of Forms comes from, if not from sense-perceptions, is our existence as unembodied souls prior to this life (Baltzly 2106: F5.2-6).  To me, this explanation sounds like a ‘retrofit’ to solve a consequential problem with Plato’s theory and is a methodological weakness of his account.

Turning now to Aristotle’s theory, whilst he shared Plato’s realism about the existence of universals, he had some fundamental differences about their ontological relationship to particulars.  In terms of Baltzly’s abovementioned description of Plato’s general argument, Plato thought that the universal, F-ness, could exist even if there were no F particulars.  In direct contrast, Aristotle held that there cannot be a universal, F-ness, unless there are some particulars that are F.  For example, Aristotle thought that the existence of the universal ‘humanity’ depends on there being actual instances of particular human beings (Baltzly 2106: F5.2-8).

As for the reality of universals, Aristotle agreed with Plato that the universal is the object of science.  For instance, the scientist is not concerned with discovering knowledge about particular pieces of gold, but with the essence or properties of gold as a universal.  It follows that if the universal is not real, if it has no objective reality, there is no scientific knowledge.  By Modus Tollens, there is scientific knowledge, and if scientific knowledge is knowledge of reality; then to be consistent, the universal must also be real (Copleston 1962: 301-302).  (Whilst it is outside the scope of this essay to discuss whether scientific knowledge describes reality, to deny that there is any scientific knowledge would have major implications for epistemic coherence).

This is not to say that universals have ‘substance’, meaning that they consist of matter and form.  Aristotle maintains that only particulars have substance, and that universals exist as properties of particulars (Russell 1961: 176).  Russell quotes Aristotle as saying:

It seems impossible that any universal term should be the name of a substance. For…the substance of each thing is that which is peculiar to it, which does not belong to anything else; but the universal is common, since that is called universal which is such as to belong to more than one thing.

In other words, Aristotle thinks that a universal cannot exist by itself, but only in particular things.  Russell attempts to illustrate Aristotle’s position using a football analogy.  The game of football (a universal) cannot exist without football players (particulars); but the football players would still exist even if they never actually played football (Russell 1961: 176).

In almost complete contrast to both Plato and Aristotle, the Stoics denied the existence of universals, regarding them as concepts or mere figments of the rational mind.  In this way, the Stoics anticipated the conceptualism of the British empirical philosophers, such as Locke (Long and Sedley 1987:181).

The Stoic position is complicated by their being on the one hand materialists, and on the other holding a belief that there are non-existent things which ‘subsist’, such as incorporeal things like time and fictional entities such as a Centaur.  Their ontological hierarchy starts with the notion of a ‘something’, which they thought of as a proper subject of thought and discourse, whether or not it exists.  ‘Somethings’ can be subdivided into material bodies or corporeals, which exist; and incorporeals and things that are neither corporeal or incorporeal such as fictional entities, which subsist (Long and Sedley 1987:163-164).  Long and Sedley (1987:164) provide colourful examples of the distinction between existing and subsisting by saying:

There’s such a thing as a rainbow, and such a character as Mickey Mouse, but they don’t actually exist.

A significant exclusion from the Stoic ontological hierarchy is universals.  Despite the subsistence of a fictional character like Mickey Mouse, the universal man neither exists nor subsists, which is a curious inconsistency.  Stoic universals are dubbed by the neo-Platonist philosopher Simplicius (Long and Sedley 1987:180) as ‘not somethings’:

(2) One must also take into account the usage of the Stoics about generically qualified things—how according to them cases are expressed, how in their school universals are called ‘not-somethings’ and how their ignorance of the fact that not every substance signifies a ‘this Something’ gives rise to the Not-someone sophism, which relies on the form of expression.

Long and Sedley (1987:164) surmise from this analysis that for the Stoics, to be a ‘something’ is to be a particular, whether existent or subsistent.  Stoic ontology is occupied exclusively by particulars without universals.  In this way, universals are relegated to a metaphysical limbo, as far as the Stoics are concerned.  Nevertheless, they recognise the concept of universals as being not just a linguistic convenience but as useful conceptions or ways of thinking.  For this reason, Long and Sedley (1987:181-182) classify the Stoic position on universals as ‘conceptualist’, rather than simply nominalist.  (Nominalists think of universals simply as names for things that particulars have in common).  In a separate paper, Sedley (1985: 89) makes the distinction between nominalism and conceptualism using the following example:

After all the universal man is not identical with my generic thought of man; he is what I am thinking about when I have that thought.

One of the implications of a particular is that it can only be in one place at any one time, which gives rise to what was referred to above by Simplicius as the ‘Not-someone sophism’.  Sedley (1985: 87-88) paraphrases this sophism in the following terms:

If you make the mistake of hypostatizing the universal man into a Platonic abstract individual-if, in other words you regard him as ‘someone’-you will be unable to resist the following evidently  fallacious syllogism.  ‘If someone  is in Athens, he is not in Megara.  But man is in Athens. Therefore man is not in Megara.’ The improper step  here is clearly  the substitution of ‘man’ in the minor premiss for ‘someone’ in the major premiss. But it can be remedied only by the denial that the  universal man  is ‘someone’.  Therefore the universal man is not-someone.

Baltlzly (2016: F5.2-15) makes that point that the same argument would serve to show that time is a not-something, yet the Stoics inconsistently accept that time subsists as an incorporeal something.

I have attempted to show above that Plato and the Stoics are locked into their theories about universals as a result of their prior philosophical positions.  Although to argue otherwise could make them vulnerable to criticisms of inconsistency, they at the same time have methodological weaknesses that place them on shakier ground than Aristotelian realism.  However, I am also of the view that apart from these methodological issues, Aristotelian Realism is substantively a better theory than Platonic Realism or Stoic Conceptualism or Nominalism.  In coming to this view, I have relied mainly on the work of the late Australian Philosophy Professor David Armstrong.

Armstrong argues that there are universals which exist independently of the classifying mind.  No universal is found except as either a property of a particular or as a relation between particulars.  He thus rejects both Platonic Realism and all varieties of Nominalism (Armstrong 1978: xiii).

Armstrong describes Aristotelian Realism as allowing that particulars have properties and that two different particulars may have the very same property.  However, Aristotelian Realism rejects any transcendent account of properties, that is, an account claiming that universals exist separated from particulars (Armstrong 1975: 146).  Armstrong argues that we cannot give an account of universality in terms of particularity, as the various types of Nominalism attempt to do.  Nor can we give an account of particulars in terms universals, as the Platonic Realists do.  He believes that ‘while universality and particularity cannot be reduced to each other, they are interdependent, so that properties are always properties of a particular, and whatever is a particular is a particular having certain properties’ (Armstrong 1975: 146).

According to Armstrong, what is a genuine property of particulars is to be decided by scientific investigation, rather than simply a linguistic or conceptual classification (Armstrong 1975: 149).  Baltzly (2016: F5.2-18) paraphrases Armstrong’s argument this way:

  1. There are causes and effects in nature.

  2. Whether one event c causes another event e is independent of the classifications we make.

  3. Whether c causes e or not depends on the properties had by the things that figure in the events.

  4. So properties are independent of the classifications that we make and if this is so, then predicate nominalism and conceptualism are false.

Baltzly (2016: F5.2-18, 19) provides an illustration of this argument based on one given by Armstrong (1978: 42-43).  The effect of throwing brick against a window will result from the physical properties of the brick and window, in terms of their relative weight and strength, independently of how we name or classify those properties.  So in this way, I would argue that the properties of particulars, that is universals, are ‘real’ rather than merely ‘figments of the mind’ as the Stoics would say.

As for Platonic Realism, Armstrong argues that if we reject it then we must reject the view that there are any uninstantiated properties (Armstrong 1975: 149); that is, the view that properties are transcendent beings that exist apart from their instances, such as in universals rather than particulars.  He provides an illustration of a hypothetical property of travelling faster than the speed of light.  It is a scientific fact that no such property exists, regardless of our concepts about it (Armstrong 1975: 149).  For this reason, Armstrong upholds ‘scientific realism’ over Platonic Realism, which he thinks is consistent with Aristotelian Realism – a position that I support.

In conclusion, I have attempted to show in this essay that the Aristotelian theory of universals is superior to the equivalent theories of both Plato and the Stoics.  I have argued this in terms of the relative methodologies as well as the substantive arguments.  I would choose the most compelling argument to be that of epistemic coherence regarding scientific knowledge, that is, that the universal is the object of science.  It follows that if the universal is not real, if it has no objective reality, then there is no scientific knowledge.  There is scientific knowledge, and if scientific knowledge is knowledge of reality; then to be consistent, the universal must also be real.


Armstrong, D.M. ‘Towards a Theory of Properties: Work in Progress on the Problem of Universals’ Philosophy, (1975), Vol.50 (192), pp.145-155.

Armstrong, D.M. ‘Nominalism and Realism’ Universals and Scientific Realism Volume 1, (1978) Cambridge: Cambridge University Press.

Baltzly, D. ATS3885: Stoic and Epicurean Philosophy Unit Reader (2016). Clayton: Faculty of Arts, Monash University.

Copleston, F. A History of Philosophy Volume 1: Greece and Rome (1962) New York: Doubleday.

Honderich, T. Oxford Companion to Philosophy (1995) Oxford: Oxford University Press.

Long A. A. and Sedley, D. N. The Hellenistic Philosophers, Volume 1 (1987). Cambridge: Cambridge University Press.

Plato, Phaedo in The Essential Plato trans. Benjamin Jowett, Book-of-the-Month Club (1999).

Plato, Timaeus in The Internet Classics Archive.
Viewed 2 October 2016.

Russell, B. History of Western Philosophy. 2nd edition (1961) London: George Allen & Unwin.

Sedley, D. ‘The Stoic Theory of Universals’ The Southern Journal of Philosophy (1985) Vol. XXIII. Supplement.

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