What is "platonism"

Platonism \Pla"to*nism\, n. [Cf. F. Platonisme.]

1. The doctrines or philosophy by Plato or of his followers.

   Note: Plato believed God to be an infinitely wise, just, and powerful Spirit; and also that he formed the visible universe out of pre["e]xistent amorphous matter, according to perfect patterns of ideas eternally existent in his own mind. Philosophy he considered as being a knowledge of the true nature of things, as discoverable in those eternal ideas after which all things were fashioned. In other words, it is the knowledge of what is eternal, exists necessarily, and is unchangeable; not of the temporary, the dependent, and changeable; and of course it is not obtained through the senses; neither is it the product of the understanding, which concerns itself only with the variable and transitory; nor is it the result of experience and observation; but it is the product of our reason, which, as partaking of the divine nature, has innate ideas resembling the eternal ideas of God. By contemplating these innate ideas, reasoning about them, and comparing them with their copies in the visible universe, reason can attain that true knowledge of things which is called philosophy. Plato's professed followers, the Academics, and the New Platonists, differed considerably from him, yet are called Platonists.
   --Murdock.

2. An elevated rational and ethical conception of the laws and forces of the universe; sometimes, imaginative or fantastic philosophical notions.

1560s, from Plato (see Platonic) + -ism.

n. (alternative case form of Platonism English)

Platonism, rendered as a proper noun, is the philosophy of Plato or the name of other philosophical systems considered closely derived from it. In narrower usage, platonism, rendered as a common noun (with a lower case 'p', subject to sentence case), refers to the philosophy that affirms the existence of abstract objects, which are asserted to "exist" in a "third realm" distinct both from the sensible external world and from the internal world of consciousness, and is the opposite of nominalism (with a lower case "n"). Lower case "platonists" need not accept any of the doctrines of Plato.

In a narrower sense, the term might indicate the doctrine of Platonic realism. The central concept of Platonism, a distinction essential to the Theory of Forms, is the distinction between the reality which is perceptible but unintelligible, and the reality which is imperceptible but intelligible. The forms are typically described in dialogues such as the Phaedo, Symposium and Republic as transcendent, perfect archetypes, of which objects in the everyday world are imperfect copies.

In the Republic the highest form is identified as the Form of the Good, the source of all other forms, which could be known by reason. In the Sophist, a later work, the forms being, sameness and difference are listed among the primordial "Great Kinds". In the 3rd century BC, Arcesilaus adopted skepticism, which became a central tenet of the school until 90 BC when Antiochus added Stoic elements, rejected skepticism, and began a period known as Middle Platonism.

In the 3rd century AD, Plotinus added mystical elements, establishing Neoplatonism, in which the summit of existence was the One or the Good, the source of all things; in virtue and meditation the soul had the power to elevate itself to attain union with the One. Platonism had a profound effect on Western thought, and many Platonic notions were adopted by the Christian church which understood Plato's forms as God's thoughts, while Neoplatonism became a major influence on Christian mysticism, in the West through St Augustine, Doctor of the Catholic Church whose Christian writings were heavily influenced by Plotinus' Enneads, and in turn were foundations for the whole of Western Christian thought.