fact that it “cannot be received in another.” Thus, too, the persons of the Trinity are, for Thomas, individuals. “The word ‘individual,’” says Thomas, in another passage, “cannot belong to God in so far forth as matter is the principle of individuation, but only in so far as the word ‘individual’ implies incommunicability” (Q. XXIX, Art. III). In this sense (Q. XXIX, Art. IV), an individual is something indistinctum, or unseparated within itself, but ab aliis distinctum, that is, set apart, by reason of its subsistence, from other individuals. The principle of individuation in case of the Trinity is the unique character of the relatio which distinguishes, for Thomas, the three persons. In God, each person is a relatio subsistens, that is, not merely an abstract relation as such, dependent upon its terms, but an individual and concrete term that subsists or is distinguished solely by its relational function. “As Deitas or Godhead is God, so the divine Paternity is God the Father.” A divine person, or person of the Trinity, signifies therefore a relation as subsistent. Thus Thomas states the case in the Summa (Q. XXIX, Art. IV): “In the comprehension of the individual substance, that is, of the distinct or incommunicable substance, one understands, in the Divine, a relation.” So far, then, one has distinction of “subsistent relations” as the principle of individuation within God. But this case is unique. Nowhere else is relation, as such, the principle of individuation.
Amongst the created rational beings, the problem of individuality becomes important in two cases.
