What is the relationship between substance and subject in Hegel’s philosophy?

In G.W.F. Hegel’s philosophy, the relationship between substance and subject is encapsulated in his famous declaration that "substance must become subject." This formula represents Hegel’s attempt to reconcile the strengths of classical and modern philosophy.1

Hegel argued that while classical Greek philosophy developed an adequate understanding of substance—viewing reality as a real, objective being—it lacked the modern appreciation for subjectivity. Conversely, modern philosophy, beginning with Descartes, prioritized the subject but failed to ground it in an objective, substantial truth.1

For Hegel, the Absolute (the all-embracing totality of reality) must be understood as both substance and subject. By this, he meant that the Absolute is not merely a static, objective "real being" or substance, but a conscious, active agent—Spirit—that realizes itself through a dialectical process. In this view, reality is not just an external object to be observed but a dynamic, rational process that unfolds through history, ultimately achieving self-consciousness.231