On Individuation

On Individuation:

The core problem of individuation is that it necessitates an account of what makes this human distinct from that human when both share one nature. It is not, however, an issue of recognising individuals as individuals, but what grounds their distinctness in reality. St. Thomas Aquinas offers a principled answer within hylomorphism; which is that individuation in material substance is grounded in matter as designated by quality. To defend this point, I will (a) define the metaphysical machinery, (b) explain how rival theories fail, (c) defend and explain why designated matter succeeds, and (d) reply to the major objections Aquinas responds to.

What to Know:

Hylomorphism - Material substances are composites of form and matter, in which form actualizes matter.

Substantial Form - what makes something the kind of thing it is (its essence as instantiated)

Matter - It is not just “stuff”, but the principle (foundational object) that can receive form.

Prime Matter - indeterminate potentiality

Designated Matter - matter under determinate dimensions

Quantity - It is not just “how much” as a measurement, but the metaphysical feature in which a body is extended and dimensioned.

Materia Signata Quantitate - matter “marked off” as this parcel by determinate dimensions

What the purpose of an individuation principle must accomplish:

An individuation principle must:

Explain how a large number of individuals can share one species while remaining numerically distinct from one another.

Maintain the intelligibility of species membership (i.e., it cannot destroy the unity of essence)

It must fit within a defined metaphysical outline of substance and accident (cannot be just a fix to an otherwise broken logical system)

Can form individuate material substances?

No, form cannot individuate material substances. Simply, form is what is common in definition across members of a species; therefore, form, by itself, cannot account for numerical multiplicity within that same species. If form individuated, then each individual would have a numerically distinct substantial form. Furthering this point, numerically distinct substantial forms would imply distinct essences, therefore undermining a species’ shared nature. Aquinas makes the point that the essence of a composite substance includes both form and matter, in the same way natural definitions do. What makes Socrates and Plato both human cannot, in itself, be what makes them numerically two. Therefore, for material substances, individuation must come from something other than form.

Can prime matter individuate material substances?

No, prime matter is pure potentiality without determinate features; to individuality, a principle must be able to account for this one versus that one. Matter, as a general concept, is not inherently this matter so it cannot do the individuating work. If matter could be individuality, it cannot be prime matter, it must be matter as determinate.

Can designated matter individuate material substances?

Yes, Individuals of the same species are numerically distinct because they have distinct parcels of matter under determinate dimensions. The metaphysical role of quantity is what makes matter divisible into here/there, this/that. It is not just an epistemic point, it is not just how we “pick out” individuals, but what makes them be numerically many. Material substances exist as extended bodies, and this sort of extension entails determinate dimensionality; therefore, designated matter is, in fact, the bridge between shared essence and numerical multiplicity. Material individuals must be “somewhere” and have determinate bodily presence, which, in turn, presupposes determinate dimensions under quantity (not just form). Therefore, any account of individuation for material substances must, then, appeal to matter as dimensioned, designated matter.

If two things have the same specific form but are informed in numerically distinct items of designated matter, they are numerically distinct individuals; due to the aforementioned claim, numerical difference is already secured by non-identity of the underlying designated matter. Therefore, distinct designed matter is sufficient for distinct individuals within one species.

In a contrasting case, Angels, or immaterial substances) lack matter, so they cannot be individuated by designated matter. Aquinas defends this point and concludes that immaterial substances are individuated by their forms (each is its own species). Aquinas, here, is not offering a one-size-fits-all rule, rather is he offering a rule keyed to the mode of being. Therefore, the principle is not arbitrary, it tracks the metaphysical structure of material vs. immaterial existence.