While I have no objection to speaking of some subjectivity or subject-as-functional-role, a foundational Subject or subject-as-unexplained-explainer is an albatross with no philosophical benefit except to make possible intriguing but ultimately untenable discourses like those of Fichte or Husserl. It gets worse when something like foundational Subjecthood is attributed to empirical subjectivity. All sorts of errors follow.

The idea of a foundational Subject was happily unknown to Plato and Aristotle. It was not in fact a requirement for Kant, who famously dwells on subjectivity, but without giving it unexplained-explainer status or assuming strong unity. It was decisively deconstructed by Hegel as a delusion of Mastery. (For a Brandomian alternative, see Scorekeeping; Mutual Recognition.)

In the early middle ages, in a more theological context, something anticipating the concept of a Subject with strong unity began to emerge in writers like Augustine and Avicenna. This proto-Subject played an important role in Christian theological notions of persons divine and human, and appears in the Thomistic notion of the intellectual soul, which in this regard owes more to Augustinian mens (“mind”) and to Avicenna than it does to Aristotle. (See also Pseudo-Dionysius on the Soul; God and the Soul; Identity, Isomorphism.)

Centuries of intensive and thoughtful theological discourse about personhood and the soul’s knowledge prepared the way for the strongly unified, foundational Subject that Descartes presented as a natural intuition, and made the cornerstone of his system. The theologians were more nuanced and interesting on this than Descartes. They wanted a stronger unity of the soul than I could philosophically countenance, but the theological context mostly prevented it from being used as an unexplained explainer. Descartes made a wreck of both philosophy and theology. (See also What Is “I”?; Substance Also Subject; Individuation; Psyche, Subjectivity; Cogito; Influence.)