"In a sense, no doubt, the separation of the "true" from the "false," the "real" from the "illusory," has been the task of thought at all times." (Willey 22). We are helped in this task to form a definition of reality by the philosophers Plato and Heracleitus, who each have contradicting views on the subject. Their views revolve around the realness of ideas and forms in relation to the realness of physical objects. .
Of the ancient Greek philosophies about reality and illusion, Plato's are the most detailed. In Plato's Theory of Forms, there is the 'World of Appearances' and the 'Intelligible World.' The world of appearances include imagining and belief. Imagining is the lowest form of perception and belief is common-sense thinking without actual knowledge. The world of appearances is unreal because it includes visible things and images. The intelligible world includes thinking and intelligence. Thinking is understanding but not quite what Plato would dub perfect knowledge. The intelligible world is real because it includes intangible things: ideas. According to Plato, reality does not change. Things that change are not real. Ideas and forms do not change ever, but physical things do. Physical objects have actions wrought upon them by outside forces or they change by themselves. Either way, their characteristics are not constant. They deceive us because the qualities we think they have are not always there at any given time. This goes against the definition of the Greek word for real, alethes. Alethes means unhidden, unconcealed, and undeceptive. Real things are only what they are and contain no contradictions; they do not deceive us. The only real things are ideas and forms. Collingwood explains the concept of Plato's unreality in The Idea of Nature:.
The sun, for example, is a dying sun, and this is only a way of saying that it has in it non-solar and indeed anti-solar characteristics, which are by degrees overcoming and ousting its solar characteristics.