In L’Être et représentation (1999), Olivier Boulnois documents the emergence of “metaphysics” in its distinctively non-Aristotelian modern sense among various 13th century authors, including Roger Bacon, Henry of Ghent, and Siger of Brabant, leading to its decisive formulation by the Franciscan theologian John Duns Scotus in the 14th century. Avicenna had already claimed that metaphysics is about “being in general”, whereas Aristotle himself had emphasized that “being is said in many ways”, which implies that there is no “being in general”.
Boulnois suggests that the 13th century authors just mentioned paved the way for Scotus’ innovations by already treating being as a concept. We are so used to that, that it is hard for us to grasp what Aristotle means in suggesting that “being in general” is not a proper concept at all.
Scotus argued against Aristotle that there is a unifying, logically minimal criterion of being, and it is representability. To be representable is to be “not nothing”. Unicorns and other imaginary creatures are representable, whereas Aristotle would not have called them beings. Scotus’ concept of representation seems to be purely logical; to have a representation of something is not necessarily to have understanding of it. For Scotus, God and creatures are equally representable, even though creatures, as finite, can be properly understood by the human mind and God, as infinite, cannot. Whereas Aristotle never speaks of an infinite being — only of a perfect one — Scotus’ generic concept of being is very explicitly indifferent to distinctions between finite and infinite.
It is one thing to acknowledge representation as a logical concept among others, and quite another to give it the kind of special first place status that Scotus does in his ontology, and that Locke does in his epistemology.
Boulnois says it is with Scotus that metaphysics became linked to what Kant later called ontotheology. While separating metaphysics as the account of being from theology as the separate account of God, Scotus also made God indifferently one of the objects of metaphysics, along with all the other beings. The combination of these changes actually brought metaphysics closer to revealed theology, and helped it to be perceived as the safe handmaiden of the later Latin tradition, rather than as independent philosophical theology that some found threatening.
If one speaks of a subject of representation, it could be — in a sense of “subject” closer to that of Aristotle — that in which something stands for something, or it could be — in a modern sense — the one who represents. “In the context of representation, the soul is not the content of its thought, but rather has a representation, distinct from itself” (Boulnois, op. cit., p. 152, my translation).
It seems that for both Scotus and Locke, the mind has representations. The soul in Aristotle is thoughts and feelings and capabilities, not something standing behind them. (See also Repraesentatio; Ontology; Being, Existence.)