The corollary of any theory of universals is an account of particulars, or individuals. A full account of individuals would answer a number of questions about the extension and intension of “individual.” It would also include an account of what makes something an individual. Medieval philosophers were not always aware ofthe need to account for the extension and intension of ‘‘individual,’’ but many of them embarked upon sophisticated investigations of the cause, or principle, of individuation.
The source of the search for a principle of individuation was often a theological controversy. Boethius, for example, considered the question of individuation as an aside to his discussions of the Trinity and the Incarnation. Other philosophers considered individuation in the context of the problem of individuating angels (e. g., Duns Scotus, Ord. II, d. 3, part 1).
In his On the Trinity, Boethius attempted to demonstrate that the Persons of the Trinity are not numerically distinct from one another (De trin. I). Boethius proposed that numerical distinctness is brought about by the inherence of accidents in a substance. Given that God has no accidents, and given that each of the Persons is God, it cannot be the case that the Persons are numerically distinct from one another.
The idea that accidental forms, either the whole set of them or some subset of them (such as spatiotemporal properties), make some thing an individual became part of what one scholar has called ‘‘the Standard Theory of Individuality’’ (Gracia 1984, 1994:26-28). According to the Standard Theory, (1) individuality is conceived in terms of difference or distinction, (2) the extension of the term ‘‘individual’’ is restricted to Aristotelian primary substances, and (3) the principle of individuation is either due to one or more accidents or to the collection of all properties (including non-accidental ones) belonging to the substance. The Standard Theory dominated much of the thinking of the early Middle Ages, although there were some notable exceptions, such as Peter Abelard and Gilbert of Poitiers.
Other medieval thinkers looked for the principle of individuation in either a substantial or a non-categorial component of individuals. A common candidate for a principle of individuation was the individual’s matter. This theory is commonly associated with Aquinas (although see Father Owen’s addendum in Gracia 1994:188). In the same vein, some medieval thinkers proposed that the matter together with the substantial form of the individual was the principle of individuation. A notable proponent of this view was Bonaventure (Gracia 1994:141-172).
Sometimes the substantial form alone was considered to be the principle of individuation. For this solution to work, the form itself would have to already be individual. One intriguing version of the notion that an individualized substantial form is the principle of individuation was hinted at by a remark in Boethius’ greater commentary on De interpretatione (in De int. 2nd edn., II, 137.3-137.16). There Boethius suggested that Socrates is individuated by a personal form, his ‘‘Socrateity.’’ It is not clear what the status ofthese personal forms is or whether Boethius really thought that these forms were the metaphysical cause of individuality, but it was interpreted this way by some later medieval thinkers.
Duns Scotus held that an individual differentia, or haecceity, is the cause of a thing being the very thing it is (Gracia 1994:284-291). Given that this haecceity does not affect or alter the formal content of the things nature, it is a non-categorial principle (King 2000:177-179).
Finally, philosophers such as Peter Abelard, William of Ockham, and John Buridan argued that there is no principle or cause of individuation (Gracia 1994:373-376 and 397-430; King 2000:180-183, and King 2004). Everything that exists is already individual. Hence, there is no need to find a cause for their individuality.
World History
