Entry 0268: Actus Essendi as Principle of Individuation (I)
Here are some excerpts from the article “Thomas Aquinas” by Joseph Owens published in Individuation in Scholasticism: The Later Middle Ages and the Counter-Reformation 1150-1650, Jorge J. E. Gracia ed., (Albany: State University of New York Press, 1994), pp. 173-194.
pp. 174-175: “From the existence that comes and goes in sensible things, existence that is accidental even though it is the basic actuality of those existents, one can reason to existence that is a nature [to God]. (See In I Sententiarum, 8, 1, 1, corpus; and De ente, 4.) Where existence is regarded as nature, the reasoning of Parmenides applies. It contains and unites everything within its own unity. It is the existence of all things, and all things have their primary existence in it. It necessarily individualizes itself. (‘Esse divinum dicitur esse omnium rerum, a quo omne esse creatum effective et exemplariter manat’ [In I Sententiarum, 8, 1, 2, corpus]. ‘Creaturae, secundum hoc quod in Deo sunt, non sunt aliud a Deo: quia creaturae in Deo sunt causatrix essentia, ut dicit Anselmus’ [In I Sententiarum, 36, 3, ad 1.]) Subsistent existence is its own individuation. (‘Ita etiam divinum esse est determinatum in se et ab omnibus aliis divisum’ [In I Sententiarum, 8, 4, 1, ad 1]. ‘Deus enim per essentiam suam est aliquid in se indivisum, et ab omnibus quae non sunt Deus, distinctum’ [De Potentia, 8, 3, corpus]. Undivided in itself and divided from others is Aquinas’ regular description of an individual, e.g., ‘Individuum autem est quod est in se indistinctum, ab aliis vero distinctum’ [Summa theologiae, I, 29, 4, corpus]). This unifying and individuating feature follows upon existence wherever it is shared.”
p. 175: “This individuating function of existence may be expressed tersely: ‘For everything in accordance with the way it has existence has unity and individuation’ (Responsio ad Fr. Joannem Vercellensem de articulis XLII, q. 108: ‘Unumquodque enim secundum quod habet esse, habet unitatem et individuationem’). Whether as subsistent in God or as accidental in creatures, existence is, in the order of being, the ‘basic cause of individuation.’ Aquinas can repeatedly insist that existence is what makes one thing differ from another: ‘As existents, however, they differ, for a horse’s existence is not a man’s, and this man’s existence is not that man’s’ (Summa theologiae, I, 3, 5, corpus: ‘Differunt autem secundum esse, non enim idem est esse hominis et equi, nec huius hominis et illius hominis’). In the language of the Liber de causis, God’s individuation is its own pure goodness. In all other things their existential actuality is the basic synthesis that makes each a unit in itself and renders it distinct from all others. The notion of an individual that emerges from these texts is the one regularly referred to by Aquinas; namely, that of an actual existent divided off from others but undivided in itself.”
p. 175: “It is expressed clearly in his early work, the Scriptum on the Sentences of Peter Lombard: ‘two features belong to the notion of an individual, namely that it be actually existent either in itself or in something else; and that it be divided from other things that are or can be in the same species, existing undivided in itself’ (In IV Sententiarum, 12, 1, 1C, ad 3: ‘…de ratione individui duo sunt: scilicet quod sit ens actu vel in se vel in alio; et quod sit divisum ab aliis quae sunt vel possunt esse in eadem specie, in se indivisum existens’). Those two features, existence as a unit in itself and its division from all other things, remain the hallmark of individuality throughout the writings of Aquinas. Existence can accordingly be called the basic ‘cause of individuality’ in his philosophical thinking. (In this context ‘cause’ and ‘principle’ have the same meaning, as with Aristotle at Metaph. IV, 2, 1003b24, though ‘principle of individuation’ came to be restricted conventionally to the order of material things.)”
p. 177: “Existence is the cause of individuation.”
p. 178: “In cases of both angel and human soul… what determines the existential actuality is what determines the individuality. Even without the body the soul continues to be an individual.”