…there are also common natures, such as human nature, which is present in each human being as his or her individual nature. Anselm holds that such common natures “become singular” when combined with a collection of distinctive properties (proprietates) that distinguish an individual from all others (Deincarnatione Verbi 11).
- Peter King, in the Encyclopædia of Philosophy
In response to an earlier post, where I wrote: "It was Christianity that identified the individual, and this well before the Enlightenment or even the Renaissance," ATL asked: “Do you know any influential works around this time that might have led to this occurrence?”
The earliest of whom I am aware is Anselm of Canterbury:
Saint Anselm of Canterbury (1033/4–1109), also called Anselm of Aosta after his birthplace and Anselm of Bec after his monastery, was an Italian Benedictine monk, abbot, philosopher and theologian of the Catholic Church, who held the office of Archbishop of Canterbury from 1093 to 1109.
Anselm has been called "the most luminous and penetrating intellect between St Augustine and St Thomas Aquinas" and "the father of scholasticism"….
Anselm writes, in The Incarnation of the Word:
…someone who cannot understand a human being [homo] to be anything except an individual shall not at all understand a human being to be anything except a human person, for every individual man is a person.
But when we say, demonstratively, “this man” or “that man,” or use the proper name “Jesus,” we designate a person—who has not only a nature but also a collection of distinguishing proper-ties by which the common human nature is individuated and marked off from other individuated human natures.
If I am recalling correctly, I believe I have read that Anselm somewhat discounted the idea of universals; however, this understanding might be a bit harsh:
While the extent of Anselm’s metaphysical realism is a matter of debate, remarks such as these make it clear that he countenanced some form of realism about universals.
Expanding on this, and again developing his concept of the individual:
In the case of substances, Anselm holds that common names designate common natures, while proper names designate individuals metaphysically composed of a nature combined with distinctive properties with further accidental qualities.