Duns Scotus’s Principle of Individuation

The “doctor subtilis,” Johannes Duns Scotus, fresco from ca. 1350

The extra-mental universal constitutes the common nature of the world (natura communis), whereas there is also a principle of individuation, namely “thisness” (hæcceitas). The common nature is common in that it is indifferent to its existence simultaneously in any number of individuals. But it has extra-mental existence only in the particular things in which it exists, and in them it is always contracted by the principle of hæcceitas. So the common nature humanity exists in both Socrates and Plato, although in Socrates it is made individual by Socrates’s hæcceitas and in Plato by Plato’s hæcceitas. The humanity-of-Socrates is individual and non-repeatable, as is the humanity-of-Plato; yet humanity itself is common and repeatable, and it is ontologically prior to any particular exemplification of it. And hence we may only venture to say on the basis of the totality of humankind what constitutes the human aspect of the common nature.

–Johannes Duns Scotus, Ordinatio lib. 2, d. 3, pars 1 (ca. 1300 CE)