Greek philosopher Plato developed his theory of Ideas, providing a philosophical formulation of the concept of the ultimate reality.

Plato’s concept of eidos, meaning “vision” in Greek, has influenced thinkers from Aristotle to medieval scholastics and theologians to modern philosophers such as René Descartes, Baruch Spinoza, Gottfried Wilhelm Leibniz, and even the twentieth century German mathematician Gottlob Frege. Plato
Socrates

The Forms, or Ideas, are the penultimate reality of things. The Platonic realm of ideas contains the pure Forms of mathematical entities, such as numbers and geometrical shapes, and moral and aesthetic ideas, such as “the just,” “the beautiful,” and “the good.” These Forms are immutable and timeless, unlike phenomena in the actual world, which are shadowy, unreliable reflections of their Forms. Although humans can never fully articulate or define the Forms using limited conceptual terms, they can grasp them intuitively. The purer the mirror of the mind, the clearer the reflection received from the realm of Ideas.

In one sense, the emergence of this theory is the consummate logical expression of the classical Greek way of viewing human experience of the world, but in another, it is possible to trace the emergence of Plato’s theory in the context of pre-Socratic and Socratic thought.

For example, from Parmenides and the Sophists, Plato borrowed language for describing the nature of the Forms and their relationship to things in the actual world; from Heraclitus of Ephesus, he derived the idea of self-sufficiency and completeness of the Forms; from the Pythagoreans, he abstracted the idea of transcendence of the Forms and how the human soul has access to that heavenly realm from the lower realm of phenomena.

Plato.

(Library of Congress)

Plato’s master and spiritual father, Socrates, had sought in the later years of the fifth century b.c.e. to discover a science of life, an objective system of knowledge of life’s goals, and the means by which such goals might be achieved. While questioning his young aristocratic friends, Socrates found that no person had made this discovery, and that all people held no more than mere opinions about these ends and means of life. Yet Socrates was convinced that the technique of life was a matter of the mind’s knowing objective principles and, once they were known, communicating them rationally. At the divine level, he was convinced that they were grasped by a deity essentially good and truthful. The individual mind, or psyche, had intuitive access to these divinely known principles; moreover, Socrates believed that the psyche was obligated to bring them to explicit rational formulation in dialogue with other people. The earlier Socratic dialogues, notably the Euthyphrōn (399-390 b.c.e.; Euthyphro, 1804), Charmidēs (399-390 b.c.e.; Charmides, 1804), and Lachēs (399-390 b.c.e.; Laches, 1804) of Plato, which are generally held to be reasonably accurate descriptions of the characteristic aims and procedures of Socrates, portray him as engaged in the effort to define inductively the precise nature of the traditional Greek moral virtues of piety, temperance, and courage. Thus, implicit in the philosophical activity of Socrates is a dualism of common opinion and transcendental moral truth to which the psyche has intuitive access.

In Plato’s account of the Forms, however, there is no dualism, because the only things that genuinely exist are the Forms. Everything else, such as rocks, plants, and animals, are mere shadows of the Forms. This explains Plato’s abhorrence of poetry and the arts. If the actual world is mere shadows of the Forms, then art and poetry are shadows of shadows. Ironically, Plato himself used a poetic and fictional literary style to narrate his philosophy.

Plato, however, preferred the speculative and analytic mode of thought over imaginative ones. He argued that to speculate about the Forms, humans must avoid the realm of opinion (doxa) and embrace the science of knowledge (epitome) or the pure intellect, which uses logical inferences to abstract the truth of the Forms. Thus, Plato separated the knowing subject from the knowledge of the realm of Ideas.

The Ionian philosophical tradition had already distinguished two types of experience: that of the senses on one hand, revealing a multiplicity of distinct impressions; and that of the mind on the other, comprehending a rational pattern having the character of unity, order, and permanence. It was characteristic of the Greek mind, moreover, to value more highly, and attribute greater reality to, the static pattern of order—visualized by the mind and recognized as a recurrent feature of experience—than the continually shifting flux of concrete phenomena. Greek art and literature, especially the richly exploited store of mythical paradigms, amply exemplify this Greek preoccupation with the eternal and recurrent pattern. It is consistent with this intellectual perspective that the Pythagorean community of southern Italy discovered that meaningful patterns of sense-experience are based on mathematical relations grasped not by the senses but by the psyche alone in inner vision. It was thus the Pythagoreans who distinguished the universal (the triangle, the square, the circle), seen by the mind alone, from the particular mode of the universal seen by the eye and found meaningful only by virtue of the psyche’s grasp of the universal.

Plato, who spent some time following the death of Socrates in 399 b.c.e. in southern Italy and Sicily in company with Pythagoreans, appears to have brought together the Pythagorean idea of the universal and the Socratic idea of the objective and eternally valid moral concept. All meaningful patterns of human experience, Plato felt, must be founded on an eternal Form or Idea known by the psyche through intuitive experience and recognized by the senses as immanent in or imitated by concrete particular objects or phenomena. In the Menōn (388-368 b.c.e.
; Meno, 1769), a transitional dialogue between his early and middle period, Plato gave the first clear formulation of this doctrine in terms of Orphic-Pythagorean dualistic mysticism. The doctrine is given ample expression in several dialogues of the middle period of Plato, notably in Phaedōn (388-368 b.c.e.; Phaedo, 1675) and Politeia (388-368 b.c.e.; Republic, 1701). The destiny of the individual psyche is a function of its participation in successive life-periods, in two distinct realms of experience: a transcendental realm in which the psyche, free from the bodily limitations of sense-experience, apprehends the eternal forms in their purity, and a physical realm of generation and corruption in which the psyche, through the bodily medium of the senses, apprehends imperfect and perishable concrete exemplifications of eternal forms. The function of philosophers is to purify their vision of the eternal forms in their ideal transcendental order so that in the physical realm they may creatively order their own lives and, if permitted, the lives of their human community, in accordance with this vision.

Plato was keenly aware of the difficulties and paradoxes involved in his notion of Forms. There are allusions to these difficulties throughout his work, especially in Parmenidēs (388-368 b.c.e.; Parmenides, 1793) and Meno, where learning and teaching become paradoxical because humans are supposed to have access to knowledge of the Forms before their experience with the world.

The impact of this doctrine on the history of philosophy, however, is immeasurable. Some believe that philosophy started with Plato’s famous dialogues. With certain modifications, Aristotle made it the basis of the first great systematic understanding of all human experience. The ontological status of Forms, be they mathematical concepts or moral ideals, has been a major subject of controversy between opposing philosophical schools throughout the Western tradition, and empiricists’ logical objections to the Doctrine of Ideas have never fully succeeded in dismissing its cogency and appeal as a necessary foundation for a secure epistemology.

• Beck, Martha C. Plato’s Self-Corrective Development of the Concepts of Soul, Forms, and Immortality in Three Arguments of the “Phaedo.” Lewiston, N.Y.: E. Mellen Press, 1999. Examines Plato’s philosophy, including his views of the Forms.
• Fine, Gail. On Ideas: Aristotle’s Criticism of Plato’s Theory of Forms. New York: Clarendon Press, 1993. A rigorous and insightful account of how Aristotle incorporated his teacher’s conception of the Forms.
• Fine, Gail, ed. Plato 1: Metaphysics and Epistemology. New York: Oxford University Press, 1999. Examines Plato’s theories of metaphysics, including forms.
• Hare, R. M. Plato. New York: Oxford University Press, 1989. Written by an eminent philosopher, this book lucidly and briefly describes Plato’s major theories. Especially see chapter 6, “Definition, Dialectic, and the Good.”
• Morgan, Kathryn A. Myth and Philosophy from the Pre-Socratics to Plato. New York: Cambridge University Press, 2000. Provides background to Plato’s philosophical ideas by describing those that came before him.
• Reynold, Noel. Interpreting Plato’s “Euthyphro” and “Meno.” Provo, Utah: Brigham Young University Press, 1988. A comparative look at different notions of the Forms in Euthyphro, Meno, and other dialogues.
• Ross, William David. Plato’s Theory of Ideas. 1951. Reprint. Westport, Conn.: Greenwood Press, 1976. An account of the development and ramifications of Plato’s theory.

Aristotle; Heraclitus of Ephesus; Plato; Pythagoras; Socrates. Ideas, theory of (Plato)