Principle of individuation

[2] It was much discussed by the medieval philosopher Duns Scotus (c. 1266–1308) with his "haecceity" and later, during Renaissance, by Francisco Suárez (1548–1617), Bonaventure Baron (1610–1696) and Leibniz (1646–1716).

Taking issue with the view expressed in certain Platonic dialogues that universal Forms (such as the Good, the Just, the Triangular and so on) constitute reality, Aristotle (384–322 BC) regarded an individual as something real in itself.

In a passage much-quoted by the medievals, Aristotle attributes the cause of individuation to matter: The whole thing, such and such a form in this flesh and these bones, is Callias or Socrates; and they are different owing to their matter (for this is different), but the same in species, for the species is indivisible.

[2]The late Roman philosopher Boethius (480–524) touches upon the subject in his second commentary on Porphyry's Isagoge, where he says that things which are individuals and are discrete only in number, differ only by accidental properties.

[3] Philosopher Avicenna (980–1037) first introduced a term which was later translated into Latin as signatum, meaning 'determinate individual'.

The nominalist philosopher William of Ockham (1287–1347) regarded the principle as unnecessary and indeed meaningless, since there are no realities independent of individual things.

The formal unity, however, is not an arbitrary creation of the mind, but exists in the nature of the thing before any operation of the understanding.