As we said before, medieval thinkers understood that words signify concepts which in turn, refer to things. Throughout the Middle Ages, philosophers and logicians debated whether concepts as universal (and signified by universal terms) refer to anything outside the mind beyond collections of individual particulars and if so, how. The issue is important because logic concerns itself primarily with words as a means to clarify concepts, and so it can seem to be a purely abstract exercise divorced from real things existing apart from human minds. What became known as “The Problem of Universals” occupied many medieval thinkers since Porphyry raised it at the very start of the medieval period in the beginning of his Isagoge or introduction to Aristotle’s Categories:
I shall refuse to say whether genus and species [these are two kinds of universal] are subsistent or located only in naked concepts. And if subsistent, whether they are corporeal or incorporeal, and if incorporeal whether separate from sensible things or subsisting in them or around them. That business is very deep and requires a greater examination.
Though Porphyry did not settle the issue, since it belongs to metaphysics (as we will see below), that did not stop medieval thinkers who adopted his Isagoge as a core textbook of the Liberal Art of Logic from mulling over the apparent paradox of universal terms and concepts. The problem is this: does the term dogness, i.e., the species “dog,” signify anything more than the collection of all dogs, something real over and above all dogs, which they all share in common? This is what Porphyry means by subsistent: something that exists in reality, apart from any mind that has a concept of dogs. Or, Porphyry asks, is dogness just a name or a concept that the mind universally applies to the collection of all dogs, a concept we create as a convenient way to group things as we see fit (whether or not they have an intrinsic connection with each other). Further, if universals are real and subsistent, are they physical or nonphysical, and if nonphysical, are they somehow in or around physical things? He seems to have primarily two extreme views in mind: the conceptualist or nominalist view for which universals are just concepts or common terms (names (in Latin nomina)) that humans devise and impose on intrinsically unrelated individuals in reality. The opposite extreme is the position that universals really exist outside the mind, but they are nonphysical and separate from material, sensible particulars. This position is associated with Plato and came to be called Extreme or Platonic Realism. Porphyry also seems to consider a third position in which universals are incorporeal and subsistent, but not separate, somehow subsisting in sensible, material individuals, which perhaps he attributes to Aristotle. Porphyry does not endorse any of these views, since as he says, it is very deep and requires greater examination. Saint Thomas following Aristotle, takes a very definite stand on the issue, and it colors what they say about predication and the predicaments or categories, and the value of logic as a tool for understanding the truth of things.
Form or species
In a way, the whole history of philosophy is wrapped up in the Problem of Universals, for it recapitulates the problem of the one and the many, of the permanence and universality of knowledge versus the particularity and constant mutability of material things bequeathed to the ages by the ancient Greeks. In the fifth century before Christ, philosophy began as the perennial search for explanations for the regularity yet variability of the natural world we experience every day, explanations provided by reason and not the divine inspiration of poets like Homer and Hesiod with their myths of gods and goddesses embroiled in all too human conflicts.
The world as our senses perceive it seems restless and unstable. … Philosophy started in the faith that beneath this apparent chaos there exists a hidden permanence and unity, discernable, if not by sense, then by mind.[1]
Beginning with Thales’ declaration that all is water, the first philosophers variously proposed different kinds of things as the ultimate hidden fabric for the changing reality we experience: for Anaximander, it was the apeiron – an indefinite, unlimited, infinite something beneath or behind the recognizable elements; for Anaximenes it was air, rarified or condensed; for Empedocles, the mixture of the four elements – earth, air, fire, and water – plus love and strife to join or separate them; for Democritus, tiny, indivisible, imperceptible atoms (literally, ‘the uncut’) swirling in the void; among other early theories.
Heraclitus advanced beyond seeking for an ultimate stuff and had the insight that the senses only ever showed a world of constantly changing material particulars incapable of ever being known beyond the fact that all is flux and that change is the only constant. One cannot, as he famously says, step into the same river twice; as a river is never the same moment to moment but flows ever on and on, so is everything material, and nothing is ever encountered twice. Much less is anything stable enough to correspond to what we claim to know. This view, along with atomists contention that physical things are just collections of imperceptible atoms, led Sophist like Protagoras to assert the there is no objective knowledge, but that ‘man is the measure of all things,’ assigning to each its meaning and truth, a position similar to the nominalist or conceptualist position described by Porphyry above.
Pythagoras, on the one hand, countered this view and focused on the fact that unchanging knowledge is indeed real and is shared in or common to all knowing minds. For example, all who understand right triangles understand his eponymous theorem – that the square of the hypotenuse is equal to the sum of the squares of the two sides (a2+b2=c2) – understand a feature common to all right triangles, and understand the same thing about these figures that all others who understand triangles do; each person’s understanding is not a private fancy, but a common grasp of the same feature common to all right triangles. Arguing in a similar vein, Parmenides took the mind’s focus on permanence to the extreme and asserted that what-is can only come from what-is-not, i.e., nothing, and since nothing comes from nothing, change is impossible and all is One. (We will have more to say about Parmenides and the Problem of Change in the next chapter on the Philosophy of Nature.)
The Heracliteans maintained that everything in the world of space and time was continually flowing, as they put it. Change never ceased to operate for a moment and nothing was ever the same for two instants together. The consequence of this doctrine appeared to be that there could be no knowledge of this world, since one cannot be said to have knowledge of something which is different at this moment from what it was a moment ago. Knowledge demands a stable object to be known. Parmenides on the other hand had said that there is such a stable reality, which can be discovered only through the activity of the mind working altogether apart from the senses. The object of knowledge must be immutable and eternal, exempt from time and change, whereas the senses only bring us into contact with the mutable and perishable.[2]
Plato sought to overcome this seemingly insoluble tension between the mutability and particularity of the material world we sense, on the one hand, and the permanence, universality, and immateriality of knowledge, on the other. It is from Plato that we get the terms which have defined and directed ever since the philosophical discussion about the objects of knowledge and our grasp of them in knowledge. Plato’s solution was to propose the existence of what he called “Forms” (eide (plural of eidos)) or “Ideas” as the fundamental objects of knowledge, especially as exemplified in mathematical knowledge of the sort that Pythagoras emphasized. Plato posited eide (Forms or Ideas) also of natural physical kinds like trees, human beings, or horses. Porphyry uses eidos when he is describing ‘species,’ and like ‘idea,’ these words derive from the Greek verb ‘to see’ (idein), as ‘species’ came into English from the Latin verb ‘speculare,’ also meaning ‘to see.’ These all share the root of ‘the look’ or ‘appearance’ of things by which we class them together: if it looks like a duck, that’s (probably) what it is. The term ‘genus’ comes from the Greek for tribe or clan, and means different kinds of things that are related to each other. Species and genus are the two kinds of universals at the heart of the Problem of Universals.
When Plato tries to explain how our minds can know as universal what our senses perceive as particular, he claims there exist two distinct, yet related, worlds or realms, and humans are living astride them both: the world as it appears to the senses, a world of changing and material things, the world of Heraclitus. Yet somehow the material world participates in, and reminds us of, the world of permanent and immaterial objects of our shared knowledge. Plato attempted to reconcile these two perspectives by positing that there must really be “Ideas” or “Forms” which we know, but in which material things participate. (Plato’s Ideas, it should be noted, are not the personal private possessions of each person’s mind, what we have been calling ‘concepts;’ Ideas for Plato exist in an immaterial realm, separate from both material particulars and individual human minds, and a person has contact with them through one’s soul.)
Rather agreeing more with Pythagoras, Plato proposed that there is a plurality of such immaterial objects of knowledge (e.g., numbers and geometrical figures, the universal horse, what it is to be human), but they are reflected in changing material things which participate in them. The physical circles made of bronze or marble which we experience are, indeed, circular, but they are only approximately so, since, however well-made they are, no circle made of bronze or marble or any material is truly a perfect, mathematical circle because it is, as Heracleitus shows, in a state of constant flux, or at least particular, physically different from all other circles. Thus, the ratio of a particular brazen circumference (C) to its diameter (d) is never truly pi (3.1415…), not as pi is intellectually known with mathematical precision. The object of our knowledge, what it is we know when we know, not just with our senses, but intellectually what a circle is (and how pi=C/d), what justice is (when we know that Socrates was unjustly executed), what beauty-itself is, etc., is their Form or Idea, i.e., what makes things be the sort of things they are. For Plato, the Forms or Ideas of physical things (and of mathematical truths and geometrical figures, as well as abstract notions like beauty and justice) exist in an immaterial reality, separate and apart from the things of which they are the Idea or Form – subsisting, incorporeal, apart from sensible things, as Porphyry says. There is thus in the immaterial realm the Form or Idea of Circle, the Form of Triangle, the Idea of Justice, etc. (Plato is also fond of referring to Forms as
“-itself”: the Circle-itself, Justice-itself, and so on. He also calls them ‘true being’ (literally ‘beingly being’ [ontōs on in Greek]). Plato argues for
the existence of what he calls Forms (eide), which he evidently understands as mind- and language-independent abstract entities which have all of their intrinsic properties essentially, which are also, in some sense, perfect paradigms of the qualities they are. … Hence if we have knowledge, its objects must not be sensible items at all: the objects of knowledge must be abstract, located in neither space nor time.[3]
Most people have a hard time accepting wholeheartedly Plato’s extreme realist position with regard to the status of universal concepts. Aristotle famously did not. Having been passed over for leadership of Plato’s Academy, his leading student and heir-apparent, Aristotle, left Athens to pursue observational studies of nature. As a result of these studies which focused on the mutability which material things, especially living things (plants and animals) undergo, and because of attendant philosophical and religious problems, Aristotle rejected the extreme realism of Plato’s separate, immaterial Ideas or Forms.
The hallmark of Aristotle as a philosopher is a robust common sense, which refused to believe that this world was anything but fully real.[4]
Yet, Aristotle also recognized that it is not in virtue of their physicality that material things remain one thing, the same thing over time – that they are relatively stable and possess their own identity. Rather, the principle of stability and identity, and thereby the principle by which they are knowable, is something intrinsic and inherent in things themselves, but it is not their matter. He, however, built upon what was true in Plato’s insights and continued to call this principle of stability, identity, and knowledge “form” or what will come to be known as their intrinsic essential nature. Aristotle also came to realize that this principle of knowability and identity also explains why things of the same sort are of the same sort. That is, form is why instances of red are red, circular shaped things are circular, and why dogs are dogs (and not cats), and so on. We will discuss how Aristotle comes to this realization in the Philosophy of Nature.
Aristotle proposed what has come to be known as the moderate realist or intrinsic realist position in the Problem of Universals, and this position stands behind the logic Aristotle developed and Saint Thomas employs in his philosophy and theology. Universal concepts identify the common forms or natures existing in material particulars that they share with other individuals of the same species or within the same genus but which the concept, as universal, abstracts from those features which differentiate individuals from each other – differences that arise from the matter in which the form as nature is realized.
Thomas follows the Aristotelian moderate realist solution as elucidated by Boethius in his second commentary on Porphyry’s Isagoge; Gyula Klima explains Boethius’ position:
[W]hen particular things are represented by a universal act of thought, the things exist in a particular manner, while they are represented in a universal manner, still, this need not imply that the representation is false. . .. In general, by means of the process of abstraction, our mind … is able to form universal representations of particular objects by disregarding what distinguishes them, and conceiving of them only in terms of those of their features in respect of which they do not differ from one another.[5]
Aquinas himself elaborates on this solution in his short, early metaphysical treatise, On Being and Essence, Chapter 3, where he says the essence, of themselves (considered absolutely), are neither universal or particular but abstract from any kind of being (esse (Latin for ‘to be’)). An essence exists universally in the mind when understood and predicated of many individuals, abstracting from the individuating features that each has due to their matter. And the very same essence (or form or nature) exists as a particular thing when so individuated.
The nature, however, or the essence thus understood can be considered in two ways. First, we can consider it according to its proper notion, and this is to consider it absolutely. In this way, nothing is true of the essence except what pertains to it absolutely. … Hence, if it is asked whether this nature, considered in this way, can be said to be one or many, we should concede neither alternative, for both [to be universal and to be particular] are beyond the concept of humanity, and either may befall the conception of man. … The nature considered in this way, however, has a double existence. It exists in singulars on the one hand, and in the soul on the other, and from each of these there follow accidents. In singulars, furthermore, the essence has a multiple existence according to the multiplicity of singulars. Nevertheless, if we consider the essence in the first, or absolute, sense, none of these pertain to the essence. … Nevertheless, the nature understood in this way is not a universal notion, because unity and commonality are in the notion of a universal, and neither of these pertains to human nature considered absolutely. … Human nature has in the intellect existence abstracted from all individuals, and thus it is related uniformly to all individuals that exist outside the soul, as it is equally similar to all of them, and it leads to knowledge of all insofar as they are men.
For Aquinas especially, following the path established by Aristotle, the very same essence or nature exists in one way as particular, i.e., in sensible material individuals, and in another way as universal, i.e., in the soul, vis., in the intellect through simple apprehension.
To say that humanity is that which makes all of us human beings implies that this essence is something shared by all human beings, that we all have the same essence; and in general, the essence of a thing is something it shares with others in the same kind. In this sense humanity constitutes a natural kind or species, namely the one traditionally defined as falling under the genus animal and as differentiated from other species in that genus by virtue of its members being rational. (More simply: human beings are by nature rational animals.) Thus considered, however, humanity exists, not in the world outside the mind, but as a concept.[6]
But that very same nature or essence which is understood through the concept exists first (and primarily, Aristotle insists (see below)) in sensible particulars. A thing’s nature
is said to be in the thing insofar as in the thing outside the soul there is something that corresponds to the conception in the soul. … Such a conception of the intellect has a foundation immediately in the thing.[7]
As Aquinas summarizes in his Commentary on Aristotle’s On the Soul
Universals according as they are universal, do not exist except in the soul; but the natures themselves, to which is attributed the intention of universality, exist in things.[8]
For Aquinas, then, again following Aristotle, shows that there need not be any Ideas or Forms existing in an immaterial realm, since the natures or essences of things, when abstracted from sensible materials are universal only as considered by our minds.
Thomas’s solution to the problem of universals, then, is this. To-be-a-species or to-be-a-genus is true of the nature per accidens because of our mode of knowing the forms or natures of material things. The nature as considered by us does not therefore warrant the claim that there must be additional subsistent things, out there, things like Plato’s Ideas.[9]
We will return to these ideas again when we consider the metaphysical doctrines of Aquinas, especially when we examine On Being and Essence, Chapter 4.
Thus, when Aristotle comes to explain how we classify things in logic, he starts with language: what is ‘said of’ or ‘not said of’ something else, but the goal is to identify and classify things according to their form or intrinsic essential natures. This goal is achieved through the act of predication – the act of attributing universals to subjects, which we do according to their forms, i.e., genus and species. What is said of another, i.e., predicated of something, is the universal class to which it belongs. But as Aristotle adopts the moderate realist account of universals, predications are true if they name the forms inhering or existing in particular objects.
[1] W. K. C. Guthrie, The Greek Philosophers (Harper & Row 1975), p. 23-4.
[2] Ibid., p. 88.
[3] Christopher Shields, Ancient Philosophy: A Contemporary Introduction (Routledge 2011), pp. 72, 74.
[4] Guthrie, op. cit., p. 125.
[5] Gyula Klima, “The Medieval Problem of Universals” in The Stanford Encyclopedia of Philosophy (Spring 2022 Edition), edited by Edward N. Zalta, (https://plato.stanford.edu/ entries/universals-medieval).
[6] Edward Feser, Aquinas: A Beginner’s Guide (Oneworld Publications. Kindle Edition), p. 39.
[7] Commentary on the Sentences, Bk. I, Dist. 2, q. 1, a. 3.
[8] Book II, Lecture 12, no. 380.
[9] Ralph McInerny, St. Thomas Aquinas, (University of Notre Dame Press. Kindle Edition), p. 114.
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