Passive principle
Hylē
In Stoicism, the concept of the passive principle refers to the material aspect of the universe, the underlying substance or matter of the universe. It is inert, unshaped, and has no qualities of its own. It is the raw material that the active principle works upon to create and sustain all things. In Stoic thought, the passive principle represents the physical aspect of reality—the "stuff" of which everything is made.
The passive principle is acted upon or shaped by the active principle. These two principles together explain the functioning and existence of everything in the cosmos.
The Stoics believed that everything in the universe is a result of the interaction between these two principles. The passive principle, as mere matter, has the potential to become anything, but it requires the active principle to give it form and function. Together, they account for the existence and nature of all things in the world.