Particulars

Individual things - this one and no other - and what it is that makes one of them this one.

Theme: Being and reality
Tradition: Cross-tradition
Term fixed: c. 330 BC

In plain terms

Everything you can point at is a particular: this cup, that person, this Tuesday. They are what the world appears to be made of, which makes them look like the easy half of the problem.

The difficulty shows up when you ask what makes one of them this one. List everything true of the cup and you have listed properties, and properties are shareable - another cup could match on every count. Yet it would still be a different cup.

So either something more than the properties makes a particular the one it is, or two things that matched exactly would be the same thing. Both answers have consequences people find hard to accept.

As a philosopher would put it

Aristotle's primary substances are individuals, and everything else is said of or present in them. The medieval question of individuation asks what accounts for it: matter, for the Thomists, since two things of the same form differ by being different portions of stuff; or haecceitas for Scotus, a non-qualitative thisness that contracts a common nature to this individual.

The modern form is Leibniz's identity of indiscernibles: if two things share all their properties they are one thing. Accept it, and there is nothing more to a particular than its properties. Deny it, and something non-qualitative individuates - which is either a bare substratum or a primitive thisness, both of which are posits nobody can point at.

The Vaiśeṣika tradition faced the same problem and answered it with viśeṣa, an ultimate differentiator in eternal atoms - a striking convergence with Scotus, arrived at independently and centuries earlier.

Where you meet it

Every fastener in a commercial aircraft is traceable. A bolt in a wing spar carries a part number, and behind it a batch record naming the mill, the heat treatment, the inspection and the date.

The reason is not that bolts differ in specification - they are made to be identical, and any of them will fit. It is that a defect in one melt of steel is a defect in that melt, and when a failure occurs the question is not what kind of bolt it was but which one, so that every other bolt from the same batch can be found.

The whole apparatus exists because sameness of kind does not deliver sameness of thing. A regulator that only knew types could not ground the right aircraft, and no amount of specification will identify an individual. What does the identifying is the record of a history - which is a point about particulars that a safety authority discovered by necessity.

What is actually disputed

Whether particulars are anything more than bundles of properties.

Bundle theorists say no, and take Leibniz's principle as a consequence: to be a particular is to be a co-instantiated collection, and two indiscernible things are one. The standard objection is Max Black's, that a universe containing nothing but two exactly similar spheres seems perfectly possible, and if it is, the principle is false.

Substratum and haecceity theorists accept the cost and posit something non-qualitative. The objection is that neither can be described, detected or distinguished from any other, which makes it look like a label for the problem rather than a solution. Bundle theory pays in intuitions, substratum theory pays in ontology, and the choice has not been settled in seven centuries.

Commonly confused with

individual in the political sense A particular is any single thing at all, including a puddle. The political term is about persons and their standing, and shares only the word.
concrete object Numbers and sets are particulars on most accounts and are not concrete. Being one thing rather than many is not the same as being physical.

Defined against

Universals The pair the medieval dispute is about, and the one it never resolved

Philosophers

Aristotle The individual as primary substance
Duns Scotus Haecceitas, the thisness that makes an individual this one
Thomas Aquinas Matter as the principle of individuation
Gottfried Wilhelm Leibniz No two things share all their properties
William of Ockham Individuals are all there is, and need no principle to individuate them

Works

Metaphysics Primary substance and the categories
Ordinatio Where thisness is argued for
Monadology The identity of indiscernibles, and a world of individuals
Vaisesika Sutra Viśeṣa, the ultimate differentiator
Summa Logicae The case that individuation needs no principle

Schools

Peripatetic school (Aristotelianism) Where the individual is primary substance
Scotism Thisness as the principle of individuation
Thomism Matter as that principle instead
Nominalism Individuals are all there is
Vaisheshika Viśeṣa, reached independently and much earlier

Related concepts

Universals c. 380 BC · Identity 1714 · Substance c. 330 BC · Form c. 380 BC · Relationality c. 150

Aristotle's primary substance is the individual; Duns Scotus asks the harder question around 1300, of what makes an individual individual, and names the answer haecceitas.