• Christian I. Patin

The Problem of Individuation

Updated: Dec 12, 2021


This project has been submitted for the Fall 2021 Semester of PHS 414: Epistemology at Holy Apostles College and Seminary, under Dr. Phillipe Yates.


The nature of being, indeed all things belonging to the realm of metaphysics, calls for an investigation into every aspect of that being. Whether something is, whither it is, how it is, how many of it there are, what it does—all questions pertaining to the thing itself. With respect to these questions, we owe much of this to Parmenides, the pre-Socratic philosopher who first tore into the burning questions of being and existence. Metaphysics, however, can be considered only as the whole field of a much more refined discussion over a particular aspect of a thing’s existence: Universals and the Problem of Individuation. Thus, to a much greater extent than Parmenides, the man responsible for the now thousands-year-old debate over the existence of the universals and the problem of individuation is Plato, the famed student of Socrates

Hyper Realism

Plato (427 BC – 347 BC)

For his part, Plato was the first to offer, in his work The Republic, the Allegory of the Cave. Here, the first notion of the Universal Forms was devised. The Allegory, to illustrate it briefly, presented men who are living in a dark cave. In the cave, they can see nothing but shadowy projections of a world beyond their own (that is, outside the cave). The sunlight from outside, an expression of the light of truth and of true knowledge, casts shadowy forms of the real, actual things that exist beyond the cave entrance. Anyone who has spent their lives in this cave, suggests Plato, accepts as true whatever forms are presented to them: a shadow of a cow is the only cow they have ever seen after all. But as soon as a man decides to pursue what is beyond the cave, he finds another world—a more perfect and vivid world, full of clearer and more exact manifestations of what the shadows could only poorly project.

Thus, Plato devised his concept of the forms: beings that exist on another plane of reality, which is responsible for giving expression to all beings that exist in our material world. For Plato, transcendentals like goodness, truth, and beauty were not the only things that could be considered Universals, but also “dogness,” “human-ness,” “squareness,” etc. He thought that the reason a dog, although different in appearance between Chihuahuas and Great Danes, are both dogs is because they both share and express the true and absolute form of “dogness,” albeit imperfectly. He further thought that “dogness” considered in itself was perfect, real, and existed apart from every actual dog.

This sort of philosophy, the idea that universal forms exist apart from all material things, is called Realism—but is often called Hyper-Realism, for it expresses a belief in immaterial, actual perfective beings that exist outside of our own existence. They are more real than our own reality (hence hyper-realism).

Moderate Realism or Immanent Realism

Aristotle (384 BC – 322 BC)

The idea, however, was quickly rejected by Plato’s own pupil—the famous Aristotle. Aristotle, the thinker responsible for his own philosophical movement, disagreed that the forms existed apart from beings in our own reality. He flatly denied that the forms existed on their own, in their own complete and perfect way in their own “world of forms.” Instead, he suggested that sensible objects are inherently united to their forms and that the forms themselves only exist insofar as they inhere in this or that particular being. If one considers a red apple, one is not accessing a super-existential realm of metaphysical servers and pulling down “appleness,” “roundness,” “redness,” “fruitness,” etc. Thus, universals do not exist in some world of forms, but they exist in the particulars upon which they predicate. This marrying of form and matter is called Hylomorphism, and it suggests that all sensible objects exist as a combination of prime matter and substantial form. In rejecting a super-existential world of forms, and positing that all forms must be instantiated in some sensible object, Aristotle become the first Immanent Realist—more broadly referred to as a Moderate Realist.

Aquinas (1225-1274)

St. Thomas Aquinas, who lived some 1500 years later, would accept much of Aristotle’s own hylomorphic formulation. Just as Aristotle taught, Aquinas believed that it was necessary that sensible objects possessed that hylomorphic union of Prime Matter and Substantial Form, but he does not seem to accept that all forms must be instantiated in the real world in order to exist. Aquinas takes concepts of immaterial beings such as angels, souls, and God, to be evidence of forms that are indeed not instantiated in sensible reality. He rejects all the same, however, the platonic idea of hyper-realism, opting for the moderate view that sensible objects are predicated by their forms—both essential and accidental forms—and that those forms really exist. But they exist in a twofold manner: (a) insofar as a perceiver abstracts them and recognizes them, (b) and insofar as they inhere as really present in particulars, not as independent reflections of really-existing things, but really existent in this or that instance. There is a third way, however, that Aquinas acknowledges the mode of existence of the universals: via the mind of God. As the good priest, Frederick Copleston, S.J., points out, for Aquinas:

The ideas, exemplar ideas, exist in the divine mind, though not ontologically distinct from God nor really a plurality, and, as far as this truth is concerned, the Platonic theory is justified.[1]

Aquinas, it seems, wants to accept on the one hand that the universal forms do not exist in their own realm, but that they are truly present in particulars as particulars themselves. He further points to the knowability of forms as distinct from the reality of forms, and that the forms have their origin and full inherence in the Divine Mind. Thus, a distinction is made between the ontological reality of forms versus the epistemological knowability of forms; an important difference in the inevitable discussion over individuation.

Duns Scotus (c. 1265 – 1308)

As Medieval thought progressed, some thinkers’ realism began to deviate away from moderation and toward nominalism. Such was the case with John Duns Scotus. His thought, sometimes aptly called “Scotistic Realism,” can be considered a kind of moderate realism that rejects any real distinction between the essence and existence of a thing: “it is simply false that existence (esse) is something different from essence.”[2] The real problem for Scotus, then, was whether there existed any real distinction between the form and the particular. The answer, at least for Scotus, is an emphatic “no.” It was necessary for Scotus to introduce a new term for universals expressed in particulars that gave them instantiation, that is, Scotus coined the term “haecceity” to describe the “thisness” of a particular being. Haecceity, or “thisness,” in the case of the man Socrates let’s say, is the formally distinct part of Socrates that makes him “Socrates” and not “Aristotle” without separating his human nature from that of Aristotle’s (or anyone else’s for that matter).

It is difficult to properly place Scotus on the Realism-Nominalism scale for the fact that he seems to reject important tenets of both Realism and Nominalism. As one writer points out, according to Scotus, “[i]n the physical world (outside the mind), nothing can be universal.”[3] On the other hand, Scotus accepts that there exists at least a hylomorphic relationship among all sensible beings, but he disagreed about the means by which those beings were instantiated and individuated. In such cases, Scotus thought that this Haecceity was the distinguishing characteristic, inherent in all sensible beings, that made it to be this man, and not that one, all while rejecting the real existence of universals outside the mind; whereas Aquinas considered these universals to be existent in three distinct ways as described earlier.


In stark contrast to both the ideas of Hyper-Realism and Moderate Realism is the philosophy of Nominalism. The most basic charge of nominalism states that, rather than universals existing in any way, what we call forms are really nothing more than names and word associations that have no real correspondence to anything in reality. Thus, when I perceive something that appears to have “dogness,” I am merely assigning the word “dog” to that being, “rover.” This is sometimes referred to as “predicate nominalism.”[4]

William of Ockham (c. 1285 – 1347)

In discussing Nominalism, William of Ockham is of particular import. Ockham’s own philosophy on the Universals is subsequent to Scotus both logically and in time. Although Ockham took issue with several tenets of Realism as a whole, he spent much time refuting Scotus on his rejection of a real distinction between form and haecceity as they inhere in a particular object.

For Ockham, it was unreasonable to consider universals as really existent in any meaningful way. He thinks this for two main reasons: first, Ockham thinks that if Scotus wants to adhere to Haecceities as only formally distinct from a thing’s nature (i.e., the “redness” of an apple and its redness) such that they have no real distinction whatever, then Scotus is forced to concede that he is saying something contradictory of the nature and the haecceity; namely, that the nature of a particular is repeatable among others in its species, but its haecceity is not.[5] Second, and perhaps more importantly, Ockham rejects that universal forms have any existence in the real world, as mentioned above. But, taking his cue from Scotus, he seems to understand the forms as existing as individual things in themselves. In other words, Ockham tends to treat forms not as a hyperrealist who considers them as existing in another world apart from our own, and not as a moderate realist who considers them as inhering in things as particulars, but rather, as existing in our world as necessary abstractions for the intellect, but apart from particulars. This is evidenced by Ockham’s objection that “no one thing can exist in other things (each of which are also one thing).”[6] Thus, Ockham rejects immanent realism on the basis that, as he sees it, universals can only be “one thing.” As such, that one thing (e.g., horseness, redness, etc.) cannot be distributed among many things without creating an inextricable, ontological link between all members of that thing. (In other words, it cannot be that Socrates and Plato share the form of “man” in any real way, otherwise, it would be the case that when two members of that species, Plato and Socrates, are in two different locations, for example, a contradiction would manifest itself.) This objection plays into the nominalist view of individuation.

Individuation of Matter

The respective views of the philosophers mentioned above account for a small but adequate picture of the principles behind Realism in general and Nominalism in general. One of the great problems derivative of both sides of this metaphysical debate is that of the Problem of Individuation. Namely, which properties of a thing’s existence (if any) contribute to its being this instance of a thing and not that one. In other words, why is Socrates distinct from Plato? What makes him distinct from his otherwise similar counterpart? The question is more poignant when we talk about two things that are exactly the same: the red in a stop sign and the red in an apple for example.

The first consideration will come from the Aristotelean approach of St. Thomas Aquinas, who posits (basically) that a “the world is made up of individual things,” what he calls, “primary substances.”[7] We can perceive particular qualities within each of these substances (e.g., John is a dentist, or Buster has sharp teeth). Although having sharp teeth or being a dentist can be predicated of other things, and are thus “not unique in themselves,”[8] they nonetheless also predicate certain aspects of John himself, or Rover himself. Aquinas notes then that primary substances are necessarily made up of prime matter, substantial form, and accidental form. In this way, it is true that John and Greg both share the exact same substantial form—they are both men. They may likewise share in some accidental forms as well (e.g., they may both have white hair and light skin). What makes them distinct and individual, then, must lie in the matter of which both men are made. To put it in his words, “matter is the principle of individuation.”[9] But because Aquinas also recognizes Prime Matter as pure potentiality, it is necessary for him to further qualify that individuation can only apply to designated matter, or, matter that has been informed by substantial form and accidental form. From this, Aquinas points at that the individuated being is precisely that which is composed of designated matter, substantial form, and accidental forms, such that Socrates is not “man,” but he is this man, in this body, in this place. Thus, and more succinctly, Aquinas calls it designated matter, “that which is considered under determined dimensions, ”[10] “matter as signified by quantity.”[11] So the most general description Aquinas offers for that which individuates matter is designated matter, which is itself an accidental property.

The individuation of matter in the sensible world is the primary argument for Aquinas in what has just been cited. Beyond this, however, as stated earlier, Aquinas observes the sensible world through the Moderate Realist’s lens. As such, Aquinas believes that anything sensible can be abstracted and known in the perceiver individually as well. When an observer experiences a particular thing, the observer can construct a phantasm in his own mind—a reconstruction or reflection of this or that particular. Further, one can deconstruct this thing (abstract its formal parts) to determine its composition of forms.

John Duns Scotus, although often cast as a realist in his own rite, follows his own flavor of realism, sometimes called “Scotistic Realism.” Scotus wants to accept that universals exist as they inhere in particulars—like Aquinas—but he rejects that they exist in any real way apart from the mind. He says, “the universal in act does not exist except in the intellect.”[12] Thus, Scotus does not believe that immanent universals—forms that inhere in multiple beings as a single instance—exist (excepting, by necessity, the Divine Essence, which involves three distinct persons that are numerically one).[13] It seems, however, that there is some disagreement about what Scotus really thinks about universals and how they are instantiated. On the one hand, Father Copleston thinks that Scotus makes himself clear when he says that “the universal act does not exist except in the intellect,”[14] while others, like JT Paasch, think that Scotus might have something like trope theory in mind.[15] (Trope theory is a nominalist approach to the universals that suggests that universals do not really exist in any sensible way—some models rejecting even the epistemological existence of forms—but rather that the qualities we find in beings (e.g., redness, roundness, etc.) are actually tropes; categories we use to classify things that are not exactly the same but are exactly similar. Some accuse trope theory of merely masking the universal with updated terms.)

Whatever the case, Scotus did not accept that matter itself or even designated matter, plus substantial form, plus accidental form, is what individuates any sort of matter. He rejected this because material bodies tend to change size over time. Thus, he reasoned that if matter (and physical dimension) is what makes a thing to be this one and not the other otherwise exactly similar thing, it would necessarily change “who” it is every time it underwent any sort of physical change in dimension. (The most obvious example is a person who becomes thinner or fatter).

Instead, Scotus offers a new element into the individuation equation: haecceity. Scotus recognized that if matter cannot fully account for the individuation of a thing, then there must be some other quality, inherent in every being, that makes it to be “this” one. Haecceity, or “thisness,” Scotus suggests, is the solution. With Haecceity in the equation, Scotus could comfortably allow for the idea of universals that inhere in every member of a given species without requiring that they all be enumerated quantitatively as “one-and-the-same” being, such that Socrates could be a member of the singular form “man,” but that he possesses a formal distinction—a haecceity—that makes him to be “the man, Socrates,” and not “the man, Plato.”[16] Haecceity allows Scotus to skirt the issue of the individuation with respect to material being, but he recognizes also that Haecceity and the Substantial Form are merely formal distinctions—that the two are really inseparable. As a final note: Scotus’ Haecceity is not to likened to Aquinas’ Quiddity. While Quiddity is what makes a thing to be the sort of thing that it is, Haeccaeity is what makes a thing to be this one of that sort and not some other one.

Ockham, as JT Paasch points out, “is history’s token nominalist.”[17] But he concedes that this is sometimes ambiguous because Ockham does not flatly reject forms. Against Aquinas, he doesn’t like the idea that Prime Matter is pure potentiality and common by nature. Instead, Ockham suggests that matter is particular, that it is actual. Further, he did not believe that the composition of a given particular relied in any way on form. He says, “[a]nything generated has two parts of which one is presupposed in the generation and called matter, and the other which is not presupposed which is called form.”[18] Further, since matter presupposes other matter (and not form) for it to be what it is, since its “essential parts are of themselves particulars.”[19] This leads Simona Massobrio to believe that Ockham saw no reason to ask the metaphysical question: what individuates matter?

Epistemologically, however, Ockham does a little work. On this point, there are some important considerations. First, as mentioned above, Ockham accepts that matter is actual, not potential. Second, because matter is actual, it is intelligible. However, although matter is in itself intelligible, we cannot grasp it of our own cognition, because matter cannot act directly on our senses. Thus, by this “defect in our intellect,”[20] we are forced to analogically compare what we perceive in matter to forms. Thus, although Ockham seems to let the metaphysical question of individuation rest on the fact that two individuals cannot be composed of exactly the same matter, the epistemological question involves an abstraction of the perception of particulars in order to make intelligible the material world.

The foregoing survey of perspectives offers some insight into the distinctions between the realist and the nominalist, both as regards nature of being, and the epistemological and metaphysical problems of individuation. While the moderate realist, like Aquinas, will prefer to say that designated matter gives a thing its “thisness;” and Scotus will prefer the term, “haecceity,” the inherent and essential property in the thing itself, for its “thisness;” Ockham, true to nominalist form, will say that the material composition of the thing itself is sufficient and that a material principle of individuation is not necessary (and further that any individuation one might cook up in the intellect is really merely the work of analogizing perceived particulars to non-existent forms).

[1] Fredrick Copleston, S.J., A History of Philosophy, Volume II: Medieval Philosophy from Augustine to Duns Scotus (New York: Doubleday, 1993), 154. [2] John Duns Scotus, Ox., 4, 13, I, no. 38 as quoted in Fredrick Copleston, S.J., A History of Philosophy, Volume II: Medieval Philosophy from Augustine to Duns Scotus (New York: Doubleday, 1993), 510. [3] JT Paasch, “Scotus and Ockham on Universals and Individuation,” Debates in Medieval Philosophy, n.d. [4] Ibid., 4. [5] JT Paasch, “Scotus and Ockham on Universals and Individuation,” Debates in Medieval Philosophy, n.d., 29. [6] Ibid., 24. [7] Patrick W. Hughes, “Aquinas’ Principle of Individuation,” Episteme, Vol. 2, Article 7, 54. [8] Ibid, 55. [9] Thomas Aquinas, On Being and Essence, 74, as quoted in Patrick W. Hughes, “Aquinas’ Principle of Individuation,” Episteme, Vol. 2, Article 7, 58. [10] Thomas Aquinas, On Being and Essence, 75, as quoted in Patrick W. Hughes, “Aquinas’ Principle of Individuation,” Episteme, Vol. 2, Article 7, 60. [11] Patrick W. Hughes, “Aquinas’ Principle of Individuation,” Episteme, Vol. 2, Article 7, 61. [12] Fredrick Copleston, S.J., A History of Philosophy, Volume II: Medieval Philosophy from Augustine to Duns Scotus (New York: Doubleday, 1993), 511. [13] Ibid, 511. [14] Ibid. 511. [15] JT Paasch, “Scotus and Ockham on Universals and Individuation,” Debates in Medieval Philosophy, n.d., 15. [16] For more on this, See [17]JT Paasch, “Scotus and Ockham on Universals and Individuation,” Debates in Medieval Philosophy, n.d., 24. [18] Ockham, Summula Philos. Natur., lib. I, c. 7 (OPh, VI, 155-6) as quoted in Simona Massobrio, “The Individuation of Matter in Ockham’s Philosophy,” Franciscan Studies 44 (1984), 202. [19] Simona Massobrio, “The Individuation of Matter in Ockham’s Philosophy,” Franciscan Studies 44 (1984), 203. [20] Ibid., 203.

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