<ontology> Greek term for what is seen-figure, shape, or form. In the philosophy of Plato, the eidos is the immutable genuine nature of a thing, one of the eternal, transcendent Forms apprehended by human reason. Aristotle rejected the notion of independently existing Forms and understood them instead as abstract universals. By extension, Husserl used the term "eidetic" for the phenomenological apprehension of essences generally. Recommended Reading: F. E. Peters, Greek Philosophical Terms: A Historical Lexicon (NYU, 1967).
[A Dictionary of Philosophical Terms and Names]
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