The form-matter scheme is a concept from ancient Greek philosophy that explores the relationship between the underlying "form" or essence of a thing and the physical "matter" that it is made of. This concept was central to the thinking of philosophers like Plato and Aristotle, who used it to explain the nature of reality and the way that objects and concepts exist in the world.
Plato, in particular, believed that the forms were the ultimate reality and that the material world we experience is only an imitation of the true forms. He used the allegory of the cave to explain this idea, with the forms representing the objects outside the cave and the shadows on the cave wall representing the material world that we perceive.
Aristotle, on the other hand, believed that the forms and the matter were equally real and that they were always found together in the objects of the world. He argued that the form of an object was the essential properties that made it what it was, while the matter was the stuff that the object was made of. In his view, the form and the matter were inseparable and could not exist without each other.