What was Plato's cornerstone theory that distinguished between the material world and a world of perfection?

Plato's cornerstone theory that distinguishes between the material world and a world of perfection is the Theory of Forms. This philosophical concept posits that beyond the tangible, physical objects we encounter in our everyday lives, there exists a realm of idealized forms or ideas—perfect and unchanging representations of all things. While we perceive things in the material world as imperfect and transient, the Forms represent the true essence of these entities. For instance, while many chairs exist in the physical realm, the Form of "Chairness" encapsulates the ideal characteristics of all chairs that we know. This theory underpins much of Plato's philosophy and has significant implications for his views on knowledge, reality, and existence, showing a clear distinction between the impermanent physical world and the eternal realm of Forms. Other theories listed, such as Dualism, Relativity, and Evolution, deal with different conceptual frameworks and do not focus specifically on the distinction between a perfect world and the material one as Plato's Theory of Forms does.