Haecceity: Scotus’s Answer to the Problem of Individuation
Haecceity is the "thisness" of a thing: the non-qualitative feature that makes it this individual, as distinct from its quiddity, the "whatness" it shares with the other members of its kind. The word comes from the Latin haecceitas, and the idea comes from John Duns Scotus, who offered it as his answer to the problem of individuation. Aquinas, the nominalists and the bundle theorists answered the same problem differently, and each kept hold of something true. The Many Beings Framework has a narrow jurisdiction on this question, and drawing that boundary exactly shows where the question does reach God.
Key takeaways
- Haecceity is thisness. It makes Socrates this man; his quiddity, humanity, is what he shares with Plato.
- It answers two questions at once. One principle explains why a thing cannot be divided into many of itself and why it differs from a perfect duplicate.
- Its strength and its strain sit together. It survives Max Black's two identical spheres, yet it has no content a concept can state.
- Frame-Indexed Classical Theism takes no side among creatures. Between Scotist haecceity, Thomist signate matter and bundle theory it stays neutral, since the question stays inside the created order; it applies where individuality is said of God.
What is haecceity?
Haecceity is the principle that makes an individual thing the very individual it is. Richard Cross, in his Stanford Encyclopedia entry on medieval theories of haecceity, defines it as "a non-qualitative property responsible for a substance's individuation and identity." The name comes from the Latin haec, "this." Its counterpart is quiddity (quidditas, from quid, "what"), the whatness of a thing, the nature it has in common with the other members of its kind.
Take Socrates and Plato. Both are human, so both have the same quiddity. Scotus held that this shared humanity, the common nature, is real outside the mind, and that in each man it is "contracted" by an individuating principle. As Thomas Williams summarizes the view, in Socrates humanity "is made individual by Socrates's haecceitas and in Plato by Plato's haecceitas." The humanity of Socrates cannot be repeated. Humanity itself can.
The word has a tangled history. In his Ordinatio, Duns Scotus (c. 1266–1308) speaks of the "individual difference" or the "individual entity," and the Latin haecceitas appears in his other writings. Cross credits the coinage to Scotus himself, while other references credit his followers.
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Analytic philosophy kept the word and loosened it. Robert Merrihew Adams, in "Primitive Thisness and Primitive Identity" (1979), wrote: "A thisness is the property of being identical with a certain particular individual." On that usage it is simply the property of being Socrates. For Scotus, Cross notes, the individual difference was the ground that explains why Socrates has that property.
What is the problem of individuation?
The principle of individuation, or principium individuationis, is whatever makes a thing this individual and sets it apart from others of the same kind. The question is old. Aristotle answered it with matter: Callias and Socrates, he wrote, "are different owing to their matter (for this is different), but the same in species." Two men share one form and differ because each is made of his own flesh and bone.
Scotus saw two questions inside the one. The first concerns a thing's indivisibility in itself. A common nature can be divided into many instances, each of which is fully human, while Socrates cannot be divided into several things each of which is Socrates. Scotus asked what it is "in [e.g.] this stone, by which as by a proximate foundation it is absolutely incompatible with the stone for it to be divided into several parts each of which is this stone." The second question concerns a thing's division from others, what makes this stone distinct from the stone beside it. Scotus held that one principle must answer both.
Theology pressed the question hard. In 1277 Stephen Tempier, the Bishop of Paris, condemned the view that there could not be more than one angel in a species. Cross observes that Christian Aristotelians held that view, "pre-eminently, Thomas Aquinas," because they located individuation in matter, and angels have none. If matter is what makes two members of one kind two, then two angels of one kind are impossible, and each angel must be a kind of its own.
The modern form of the same test belongs to Max Black. In 1952 he asked: "Isn't it logically possible that the universe should have contained nothing but two exactly similar spheres?" Black supposed each made of pure iron, a mile across, with the same temperature and color. If such a world is possible, something other than their qualities and relations makes the spheres two.
How did Scotus argue for haecceity?
Scotus argued for haecceity by elimination, testing each rival principle against both questions. Cross's entry walks through the cases.
Qualities could not do it. What is common to a kind cannot make one member of it this member, and the accidents a thing happens to have come after the thing itself. Which accidents it has is a matter of its history, and a thing is not the same as its life story. A negation could not do it either, because saying a thing is undivided restates the problem without explaining it. Existence failed because existence as such "does not seem to be different from case to case."
Matter and quantity came closest. Quantity can explain why two chunks of stuff are distinct, yet it cannot explain indivisibility, since "the quantitative parts into which a continuous whole is divided never admit of the predication of the whole that is divided into them." Half of this stone is not this stone, while each human being is fully human. The same matter can also persist when one substance becomes another, so matter cannot be what made the first substance the individual it was.
What remained was a positive principle of its own kind. "This individual entity is not matter or form of the composite, inasmuch as each of these is a nature," Scotus wrote. "Rather, it is the ultimate reality of the being that is matter or that is form or that is the composite."
It is formally distinct from the common nature. The two are really the same thing and cannot be separated, yet the account of one is not the account of the other. Scotus called haecceities "primarily diverse," and he said they "agree in nothing the same," which is why they can ground a difference that a shared feature could not.
His argument leaned on his realism about common natures. Because humanity has a real unity of its own, less than numerical unity, whatever makes it this humanity must be equally real. Cross judges that Aquinas denied the nature considered in itself any such unity, which places Scotus further toward realism than Aquinas stood.
What are the rival answers to the problem of individuation?
The rival answers are matter, self-individuation, bundle theory with the identity of indiscernibles, and, in modern dress, haecceitism, and each keeps hold of something true.
Matter. Aquinas located individuation in matter. In De ente et essentia he wrote that "only signate matter is the principle of individuation. I call signate matter matter considered under determinate dimensions." Signate matter would belong to the definition of Socrates "if Socrates had a definition," so this flesh and these bones make this man. What the view gets right is how bodies of one kind are many, and it belongs to the account of matter and form at the center of Thomism. Aquinas's formulation varied across his works, and in the Summa Theologiae he drew the consequence for angels: "it is impossible for two angels to be of one species."
Self-individuation. Peter Auriol and William of Ockham, writing soon after Scotus, held that things are singular of themselves and need no added principle. Francisco Suárez later held that every being is individual by reason of being a thing. What this view gets right is economy. It declines to add an entity to explain a fact that may be basic.
Bundle theory and the identity of indiscernibles. Bundle theory, associated with David Hume, holds that "an object consists of its properties and nothing more." Its natural ally is the identity of indiscernibles, the thesis, in the words of the Stanford Encyclopedia entry on the principle, "that there cannot be numerical difference without extra-numerical difference." Leibniz put it as a claim about resemblance: "It is not true that two substances resemble each other entirely and differ solo numero." What this view gets right is that what we can know and say of a thing is its qualities. Black's spheres are its standing test.
Contemporary haecceitism. Analytic metaphysics asks a modal version of the question. Haecceitism, in Sam Cowling's formulation, is the thesis that "the world could differ non-qualitatively without differing qualitatively." Anti-haecceitists deny it. David Kaplan credited the label to Robert Adams, and Cowling notes that haecceitism does not by itself commit anyone to haecceities as entities.
Where is haecceity strong, and where does it strain?
Scotus's answer is strongest where its rivals come under the most pressure and thinnest where it must say what the principle is. It answers his two questions with one principle, so the account of why Socrates is one and the account of why he is not Plato are the same account. It survives Black's spheres, because two spheres alike in every quality and relation can still differ in their individual principles. Cross observes that this keeps a trivial reading of Leibniz's principle true and gives up the reading Leibniz intended. It also keeps kinds real without turning an individual into a bundle.
The strain lies in what the principle is. It is not a qualitative feature and adds no further content to what a thing is. In the words of the Wikipedia article on the term, it "differs from the specific differentia by not having any conceptually specifiable content." We can point to it as "whatever makes this thing this," and beyond that phrase a concept has little to state. The principle is secure as an answer to what must be there and thin as an answer to what it is.
Scotus's near successors saw the point. Peter Auriol, as the Stanford Encyclopedia quotes him, held that "maintaining that an object is singular or individual because it results from or is endowed with a proper principle of individuation which is itself singular, amounts to nothing more than duplicating what should be explained." If the haecceity of Socrates is itself singular, the question of what makes it singular returns.
Two further difficulties press from inside the view. The first is what Cross calls Ockham's problem: if the common nature has a real unity less than numerical, it is hard to say where that unity is once the nature exists in two individuals. The second came from the Thomist Cajetan, who argued that haecceities would have to be more or less alike, those of Socrates and Plato more alike than Plato's and a patch of white. That sits uneasily with Scotus's claim that they "agree in nothing the same."
These difficulties leave Scotus's first claim standing, that something makes a thing this. What they press is how little can be said about it.
Volume One builds its account of natures from two axioms, before any dilemma is in view; read it free.
What does Frame-Indexed Classical Theism say about haecceity?
Frame-Indexed Classical Theism (FICT) is a research program in analytic theology that resolves classical theological dilemmas by diagnosing them as artifacts of a single formal error, and here it takes no side between Scotus's principle and Thomist signate matter, since that question stays among creatures. It speaks where individuality is said of God. It is the position of the Many Beings Framework and the most immediate contemporary heir of Thomistic analogical predication. It rests on two axioms: a being's nature is the fusion of its essential qualities, and a conscious being's mode of existence determines its mode of apprehension. From God's frame, the Absolute Metaphysical Frame, there is one unified reality, known whole. The Human Finite Frame receives that same reality in parts and in sequence, knowing God truly by the intellect without apprehending Him perceptually as He apprehends Himself.
The framework's rule governs words said across the boundary between Creator and creature, and for the problem Scotus posed individuation does not cross it. What makes this man this man and not his twin is asked and answered among creatures of one kind. Scotist haecceity, Thomist signate matter, self-individuation and bundle theory are rival accounts of the created order, and the framework does not decide between them.
Three things the framework holds lie close by. First, it defines a nature as the fusion of a being's essential qualities, its "what-it-is-ness." That is a claim on the side of quiddity: it tells us what a man is and leaves open what makes this man this one.
Second, it counts identity among the terms that keep one sense in both frames, so "this stone is this stone" is true in God's frame in the same sense as in ours. Third, from God's frame the one reality is known without ignorance, and that knowledge includes each creature. Isaiah joins them:
"To whom will you compare me? Or who is my equal?" says the Holy One. Lift up your eyes and look to the heavens: Who created all these? He who brings out the starry host one by one and calls forth each of them by name. Because of his great power and mighty strength, not one of them is missing. (Isaiah 40:25–26, NIV)
The question does cross the boundary when individuality is said of God. Natures shared by many bearers, properties and universals are the right apparatus for creatures, which are composite and belong to kinds, and Volume Four grants that apparatus its full truth in the finite frame. Scotus's principle makes one instance of a shared nature this instance. To ask for its counterpart in God fits the Creator into a taxonomy built for things that instantiate a kind, and the framework declines that demand as it declines to make God either a bearer of properties or a property. Aquinas drew the same line in the Summa: "God cannot be called an 'individual' in the sense that His individuality comes from matter; but only in the sense which implies incommunicability."
What distinguishes the divine persons belongs to God's life with Himself, and there the framework offers no account. It receives the doctrine of the Trinity as the church confesses it. Its contribution here is a boundary drawn precisely, silent on whether Scotist haecceity or Thomist signate matter individuates creatures and exact about where "individual" may be said of God. The Frame-Indexed Classical Theism page sets out the axioms and the rule.
Volume Four takes up divine simplicity and Scotus's formal distinction in Resolving Immutability & Interaction.
How the answers compare
Each answer keeps something the others need, and the comparison turns on what each leaves open.
| Position | What makes this thing this | What it gets right | What it leaves open |
|---|---|---|---|
| Scotist haecceity | A non-qualitative principle, formally distinct from the common nature | One principle for indivisibility and distinction | What the principle is, beyond its role |
| Thomist signate matter | Matter under determinate dimensions | How bodies of one kind are many | Angels, and what individuates matter |
| Self-individuation (Auriol, Ockham, Suárez) | No added principle | Economy | Why things of one kind resemble one another |
| Bundle theory and identity of indiscernibles | Qualities and relations | We know a thing through its qualities | Black's spheres |
| Frame-Indexed Classical Theism | Takes no side between the Scotist and Thomist answers; identity univocal in both frames | Where "individual" may be said of God | The creaturely question itself |
Frequently asked questions
What is the difference between haecceity and quiddity?
Quiddity is a thing's whatness, the nature it shares with others of its kind. Haecceity is its thisness, what makes it this individual. Socrates and Plato have one quiddity, humanity, and two haecceities. In Scotist usage the individual difference adds no further content to the quiddity. It determines the kind to one unrepeatable instance, much as a specific difference determines a genus to a species.
What is the principle of individuation?
The principle of individuation is whatever makes a thing this individual and distinct from others of its kind. Among medieval thinkers, Aristotle's heirs including Aquinas proposed matter, Henry of Ghent a negation, Durandus actual existence, and Scotus the haecceity, while Auriol, Ockham and Suárez held that a thing is individual of itself. Modern discussion carries the question through bundle theory, the identity of indiscernibles and haecceitism.
What is haecceitism?
Haecceitism is the modal thesis that the world could differ in which individuals exist, or in which individual plays which role, without differing in any quality. Cowling's example imagines a world where a qualitative duplicate of you, Double, exists in your place. The haecceitist counts that a genuine possibility, and the anti-haecceitist does not. The view takes its name from Scotus's term, yet it does not by itself require haecceities as entities.
Did Aquinas believe in haecceity?
No. Aquinas held that signate matter, matter under determinate dimensions, is the principle of individuation for material things, and he concluded that each angel is its own species. Scotus wrote after him and rejected matter as the individuator, in part because the same matter persists through substantial change. The two also differ over the common nature, which Scotus treated as having a real unity of its own and Aquinas did not.
Does God have a haecceity?
Not in the sense Scotus gave the word. Scotist haecceity makes one instance of a shared nature this instance, and Thomist individuation runs through matter, so neither applies to God as it applies to creatures. Aquinas allowed God to be called individual only in the sense of incommunicability. Frame-Indexed Classical Theism agrees and gives the reason: asking for God's haecceity fits the Creator into a taxonomy of bearers and instances built for creatures. What distinguishes the divine persons lies outside the framework's account.
Where to go from here
Scotus showed that something must make a thing this, and his critics showed how little can be said about what it is. The question worth carrying into theology is where the word may be said and where it may not. Among creatures of one kind the rival accounts still contend, and the Many Beings Framework leaves that contest to them. Where "individual" is said of God, the framework holds the line Aquinas drew and states the reason for it.
Volume One sets out the two axioms, derives the frames and names the Many Beings Fallacy, and it is free to download. Volume Four, Resolving Immutability & Interaction, takes up divine simplicity, properties and Scotus's formal distinction, and it is available now. The rest of the series carries the same rule through the problem of evil and time and eternity.
