Terminology: the Forms and the forms
The English word “form” may be used to translate two distinct concepts that concerned Plato—the outward “form” or appearance of something, and “Form” in a new, technical nature, that never
…assumes a form like that of any of the things which enter into her; … But the forms which enter into and go out of her are the likenesses of real existences modelled after their patterns in a wonderful and inexplicable manner….
The objects that are seen, according to Plato, are not real, but literally mimic the real Forms. In the allegory of the cave expressed in Republic, the things that are ordinarily perceived in the world are characterized as shadows of the real things, which are not perceived directly. That which the observer understands when he views the world mimics the archetypes of the many types and properties (that is, of universals) of things observed.
[edit]What are the Forms?
The Greek concept of form precedes the attested language and is represented by a number of words mainly having to do with vision: the sight or appearance of a thing. The main words, εἶδος (eidos) and ἰδέα (idea)[7] come from the Indo-European root *weid-, “see”.[8] Both words are already there in the works of Homer, the earliest Greek literature. Equally ancient is μορφή (morphē), “shape”, from an obscure root.[9] The φαινόμενα (phainomena), “appearances”, from φαίνω (phainō), “shine”, Indo-European *bhā-,[10] was a synonym.
These meanings remained the same 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 quite a bit and began to ask what the thing changing “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?