The importance of signs and signification has been recognized throughout much of the history of philosophy, and in psychology as well. The term derives from the Greek: σημειωτικός, "sēmeiōtikos", "observant of signs" (from σημεῖον "sēmeion", "a sign, a mark"). For the Greeks, "signs" occurred in the world of nature, and "symbols" in the world of culture. As such, Plato and Aristotle explored the relationship between signs and the world.