Theory of Forms

Plato's theory of Forms or theory of Ideas argues that non-physical (but substantial) forms (or ideas) represent the most accurate reality. When used in this sense, the word form or idea is often capitalized. Plato speaks of these entities only through the characters (primarily Socrates) of his dialogues who sometimes suggest that these Forms are the only objects of study that can provide knowledge; thus even apart from the very controversial status of the theory, Plato's own views are much in doubt. However, the theory is considered a classical solution to the problem of universals.

The early Greek concept of form precedes attested philosophical usage and is represented by a number of words mainly having to do with vision, sight, and appearance. The words, εἶδος (eidos) and ἰδέα (idea) come from the Indo-European root , "see".Eidos (though not idea) is already attested in texts of the Homeric era, the earliest Greek literature. This transliteration and the translation tradition of German and Latin lead to the expression "theory of Ideas." The word is however not the English "idea," which is a mental concept only.

The meaning of the term εἶδος (eidos), "visible form", and related terms μορφή (morphē), "shape", and φαινόμενα (phainomena), "appearances", from φαίνω (phainō), "shine", Indo-European *bhā-, remained stable over the centuries until the beginning of philosophy, when they became equivocal, acquiring additional specialized philosophic meanings. The pre-Socratic philosophers, starting with Thales, noted that appearances change, and began to ask what the thing that changes "really" is. The answer was substance, which stands under the changes and is the actually existing thing being seen. The status of appearances now came into question. What is the form really and how is that related to substance?

Thus, the theory of matter and form (today's hylomorphism) was born. Starting with at least Plato and possibly germinal in some of the presocratics the forms were considered as being "in" something else, which Plato called nature (physis). The latter seemed as carved "wood", ὕλη (hyle) in Greek, corresponding to materia in Latin, from which the English word "matter" is derived, shaped by receiving (or exchanging) forms.

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