Plato developed his Theory of Ideas to address the question "What is truly real?". He proposed that there are universal ideas that represent perfect forms, like the ideal "Cat", that are eternal and immutable. Particular objects in the world only imperfectly represent these ideas. Plato distinguished between knowledge gained through reason and intellect versus opinion from sensory perception. His metaphysical system included eternal ideas that represented true reality, and changing physical phenomena. Plato also developed a hierarchy of knowledge and a tripartite theory of the soul to explain human understanding and fulfillment. Later philosophers like Ibn 'Arabi drew upon Plato's ideas in developing their own spiritual frameworks and understanding the stages of human and cosmic evolution.