Idea

For Plato, ideas or Forms are not mental contents but eternal, unchanging realities that constitute a realm of intelligible being, distinct from the sensible world of becoming. Particular beautiful things come and go, but Beauty itself neither changes nor perishes. Knowledge consists in the apprehension or understanding of these intelligible objects through dialectic, and the allegory of the cave in the Republic dramatizes the ascent from sense appearances to the sunlight of the Good. The distinction between two orders of reality, the sensible and the intelligible, and two modes of apprehension, sensing and understanding, is fundamental to Plato's use of the word "idea" for both the intelligible object and the understanding of it.

The doctrine of recollection, set forth in the Meno and the Phaedo, explains how the soul comes to know what it has never learned through the senses. "There have always been true thoughts in him," Socrates tells Meno, thoughts "which only needed to be awakened into knowledge by putting questions to him." Learning, on this account, is an attempt "to recollect, not what you do not know, but rather what you do not remember." This process, in which latent ideas become active through questioning or through the stimulus of sense-experience, implies a functional connection between body and soul, but the ideas themselves are independent in origin, not derived from sense. The question of innate ideas, treated more fully under the idea of Knowledge, receives its first formulation here.

The theory of Forms raises difficulties that Plato himself acknowledges in the Parmenides. The argument between Aristotle and Plato about the being of the Ideas or Forms apart from both matter and mind is considered more fully under the idea of Form. The traditional epithet "realism" gets one of its meanings in this context, signifying the view that ideas or universals have an independent reality of their own. The various opponents of this view, whether they deny any existence to universal ideas outside the mind or deny the presence of universals even in the mind, are called "conceptualists" or "nominalists," as discussed under the ideas of Same and Other and Universal and Particular.

Plato's theory of Ideas sets the terms for every subsequent discussion. Aristotle denies that the Forms exist separately from sensible things; Plotinus places them in the divine Intellect; and the modern empiricists from Locke to Hume define their positions by denying any connection between ideas and a transcendent realm of being.

For Aristotle, ideas or concepts have no being except as thoughts in the mind, and they are the instruments whereby reality is known. The intellect does not ascend to a separate realm of Forms; it abstracts the universal from the particular by drawing "the intelligible species" from sensory images, which Aquinas later calls "phantasms." The concepts by which "our intellect understands material things," we obtain "by abstracting the form from the individual matter which is represented by the phantasms." The soul in knowing becomes, in a sense, the form of the thing known, without the matter, and it is for this reason that "the soul never thinks without an image."

Aristotle's critique of Plato in Metaphysics I is direct. If the Forms exist separately, they explain nothing about the things we actually encounter. They become a redundant doubling of the world. Separate Forms cannot cause the existence or intelligibility of their instances, because a cause must be in some way present to what it causes. The argument between Aristotle and Plato about the being of the Ideas apart from both matter and mind is discussed more fully under the idea of Form.

Abstract or universal concepts occupy, on Aristotle's account, an intermediate position between the ideas that belong to intellects separate from bodies and the particular perceptions or images of sense. Conception, which is the first act of the mind, yields knowledge only when concepts are used in subsequent acts of judgment and reasoning. The resemblance between Aristotle's position and that of William James, each affirming in his own way that the mind contains nothing not rooted in the senses, serves to mediate between the more extreme positions in the tradition. The question of the origin and derivation of ideas in the human mind is treated also under the ideas of Mind and Knowledge.

Aristotle's abstraction theory becomes the dominant framework for medieval thought through Aquinas, who will explain in detail how the agent intellect abstracts the intelligible species from the phantasms. Descartes will challenge this framework by endowing the human mind with innate ideas that are not derived from sense-experience at all.

Plotinus places the Platonic Forms within the divine Intellect (Nous), the second hypostasis of his metaphysical scheme. The One, which is beyond all thought and being, overflows into Intellect, and Intellect contemplates itself as a unity of all the Forms. The Ideas are not external to Intellect; Intellect is the Ideas. Each Form is a complete perspective on the whole, and the whole is present in each. Ideas in the order of supra-human intelligence, the eternal exemplars and archetypes, thus receive in Plotinus a definite metaphysical location that Plato's dialogues had left indeterminate.

To know an Idea, on Plotinus's account, is not to abstract from sense experience in the manner of Aristotle. It is to turn inward and upward, to participate in Intellect's self-contemplation. The soul descends from the intelligible realm into the material world but retains a connection to Nous at a level deeper than discursive reasoning. Learning is a process of recovery, in which the soul recollects what it already possesses. This bears a resemblance to the Platonic doctrine of recollection, though Plotinus develops it in the context of his own emanation theology.

Plotinus also takes from Aristotle the insight that thought and its object are identical in the highest form of knowing. But where Aristotle's divine intellect thinks only itself and remains remote from the world, Plotinus's Nous contains the Forms of all things and is the fullness of being as well as the fullness of thought. The identification of the thinking mind with the intelligible content it thinks is one of the defining positions of the Neoplatonic tradition, and it bears on the question of the being and truth of ideas discussed under the idea of Truth.

Plotinus transmits a transformed Platonism to the Christian world. Augustine will place the Ideas in the mind of God, reading Plotinus through Scripture and identifying the divine Intellect with the Word. The question of whether human minds know by participating in the eternal Ideas, and if so what the mechanism of this participation may be, is one that Augustine's theory of illumination addresses without fully resolving.

Augustine identifies the Platonic Forms with the eternal creative thoughts in the mind of God. The divine ideas, Augustine says, are "certain original forms or permanent and immutable models of things which are contained in the divine intelligence." Since "each thing was created by God according to the idea proper to it," the world is intelligible because it is the expression of a rational mind, and knowledge of things consists ultimately in a participation in the knowledge God has of his own essence. The question of ideas in the order of supra-human intelligence, of the eternal exemplars and archetypes, receives in Augustine its definitive Christian formulation.

"To learn those things which do not come into us as images by the senses," Augustine writes, "but which we know within ourselves without images is in reality only to take things that the memory already contains scattered and unarranged, and by thinking bring them together." The memory contains, not only images impressed upon it by the senses, but also "the notions of the very things themselves, which notions we never received by any avenue of the body." This theory of illumination replaces Plato's recollection: we do not remember a past life; we see by a present light. Sense-experience may occasion the awakening of the understanding, but the ideas themselves are independent in origin, not derived from sense.

Augustine tends to describe the experience of illumination more than its mechanism, and later thinkers, including Aquinas, will press the question of whether the divine light is a special intervention for each act of knowing or a permanent endowment of the created intellect. But the framework endures: ideas have their ground in the divine intellect, and human knowledge is a participation in God's truth. The question of the infusion of ideas and of divine illumination is treated also under the ideas of God and Knowledge.

Augustine's fusion of Platonism and Christianity dominates Western thought until the thirteenth century. Aquinas will introduce Aristotelian abstraction as the primary account of how the human mind acquires ideas, while preserving the Augustinian insight that the divine ideas are the ultimate ground of the intelligibility of created things.

Aquinas holds that "our intellect abstracts the intelligible species from the individuating principles," the material conditions of sense and imagination, and that the concepts by which we understand material things are obtained "by abstracting the form from the individual matter which is represented by the phantasms." The human intellect, which occupies a middle place between angelic intelligence and corporeal sense, functions only in cooperation with the corporeal powers of sense and imagination, so that "it must of necessity turn to the phantasms in order to perceive the universal nature existing in the individual." In this life, we cannot know anything without turning to sense images.

Yet Aquinas also preserves the Augustinian insight that ideas exist eternally in the mind of God as the exemplar causes of all created things. "The intelligible species in the divine intellect," he writes, "is immaterial, not by abstraction, but of itself." The divine ideas are "certain original forms or permanent and immutable models of things which are contained in the divine intelligence." The human mind does not need special divine illumination to know ordinary truths; the natural light of the agent intellect suffices. But the agent intellect itself is a participation in the uncreated light.

Aquinas carefully distinguishes the concept as "that by which the intellect understands" from "that which is understood." A concept is primarily the means of knowledge, not the object of knowledge. Secondarily, however, concepts become what we know when we reflexively turn our attention to the contents of our own mind. It is possible, therefore, to have ideas about things or ideas about ideas. The ideas whereby real things are understood are called the "first intentions" of the mind; the ideas whereby we understand these ideas are called the mind's "second intentions." This distinction bears on the question of the logic of ideas and of the relation between concepts and terms, discussed under the idea of Judgment.

Descartes and Locke will abandon the Thomistic distinction between ideas as means and ideas as objects, turning ideas into the immediate objects of awareness rather than transparent instruments of knowing. The entire problematic of modern epistemology, including the question of how the mind reaches things beyond its own ideas, follows from this shift.

Descartes endows the human mind with ideas that are not concepts abstracted from and dependent on sense, but intuitive apprehensions which, since they cannot be drawn in any way from sense-experience, must be an innate property of the human mind. Some ideas, he says, "appear to be innate, some adventitious, and others to be formed or invented by myself." The ideas called "adventitious" are those which seem to come from the outside, as when "I hear some sound, or see the sun, or feel heat." Those which we form or invent ourselves are constructions of the imagination. Only innate ideas, in Descartes' view, are truly ideas in the sense of being the elements of certain knowledge and the sources of intellectual intuition. "By intuition," he says, "I understand, not the fluctuating testimony of the senses, nor the misleading judgment that proceeds from the blundering constructions of the imagination," but "the undoubting conception of an unclouded and attentive mind" which "springs from the light of reason alone."

As mind and body are separate substances for Descartes, so ideas and sensations are independent in origin and function. Innate ideas in the human mind are not abstract, for they are not abstracted from sense-materials. The doctrine of innate ideas separates intellectual knowledge from sense-experience more sharply than any position since Plato. Sensory ideas are confused and obscure; innate ideas are clear and distinct, and their truth is guaranteed by a non-deceiving God. The question of clear and distinct ideas as criteria of truth is treated under the idea of Truth.

Descartes classifies ideas as innate, adventitious, and factitious, and the most important for knowledge are the innate ones, including the ideas of God, substance, extension, and mathematical truths. The idea of God, in particular, could not have been produced by a finite mind from its own resources, and so proves that a being of infinite perfection exists. This argument, and the general question of the relation between ideas and the reality they represent, is treated also under the idea of God.

Locke will accept Descartes' use of "idea" for whatever is the object of the understanding when a man thinks, but he will demolish the doctrine of innate ideas by arguing that all ideas derive from experience. Berkeley and Hume will develop the empiricist position further, each drawing different consequences from the premise that ideas are the immediate objects of the mind.

Locke, begging the reader's pardon for his frequent use of the word "idea," says that it is the term "which serves best to stand for whatsoever is the object of the understanding when a man thinks." But he demolishes the doctrine of innate ideas. If ideas were innate, children and the unlearned would possess them, yet they manifestly do not. There is no universal assent to the principles supposedly implanted by nature. The mind at birth is "white paper, void of all characters, without any ideas," and all its furnishings come from experience.

Experience has two channels: sensation, which delivers ideas of external objects, and reflection, which delivers "the perception of the operations of our own mind within us, as it is employed about the ideas it has got." From these two sources come all simple ideas, which the mind receives passively. The mind then compounds, compares, and abstracts them into complex ideas, but all the raw materials derive ultimately from experience. Locke distinguishes between particular and general ideas (which he calls "abstract"), and between ideas of primary qualities, which resemble qualities really in bodies, and ideas of secondary qualities, which are merely powers in objects to produce certain sensations in us. The question of whether abstract or general ideas correspond to anything real, and of how concepts relate to terms, is discussed more fully under the ideas of Universal and Particular and Sign and Symbol.

Locke also distinguishes between knowledge of real existences through ideas "that the mind has of things as they are in themselves," and knowledge of the relations among our own ideas, "which the mind gets from their comparison with one another." This double use of "idea," in which ideas are both the means of knowing reality and possible objects of knowledge in their own right, parallels the Thomistic distinction between first and second intentions, though Locke develops it within an entirely different framework.

Locke's empiricism defines the modern problem of ideas. By denying innate ideas and treating all ideas as derived from experience, he creates a framework that Berkeley will radicalize and Hume will carry to skeptical conclusions. The question of the origin and derivation of ideas in the human mind remains one of the fundamental issues in the tradition.

Berkeley insists that "the various sensations or ideas imprinted on the sense, however blended or combined together, cannot exist otherwise than in a mind perceiving them." His famous proposition, esse est percipi, is intended to permit only one exception: the perceiving mind has being without being perceived, but nothing else does. Everything else which exists is an idea, a being of and in the mind. According to this doctrine, the phrase "idea of" is without meaning, for nothing exists of which an idea can be a representation. The real and the ideal are identical. The question of the being and truth of ideas, and of the distinction between real and intentional existence, is treated also under the idea of Being.

Berkeley thinks "the objects of human knowledge" include "either ideas actually imprinted on the senses; or else such as are perceived by attending to the passions and operations of the mind; or lastly ideas formed by the help of memory and imagination, either compounding, dividing, or barely representing those originally perceived in the aforesaid ways." The "matter" that Locke posits as the unknown support of primary qualities is, on Berkeley's account, an abstraction that no one has ever perceived and no one can coherently describe. He attacks abstract ideas, general concepts separated from every particular in which they could be instantiated, as the source of much philosophical confusion.

The world persists, on Berkeley's view, because God always perceives it. The stability and regularity of our experience is guaranteed by the divine mind, which produces our ideas according to orderly laws. Their cause is neither physical matter nor the perceiving mind, but "some other will or spirit that produces them." Berkeley's idealism thus eliminates the gap between idea and thing at a stroke: what we perceive is what is real. The question of whether ideas constitute a realm of being independent of matter, or whether they exist only in the mind, is one of the central issues in the tradition, discussed also under the ideas of Matter and Mind.

Berkeley forces every subsequent empiricist to reckon with idealism. Hume, dividing all perceptions of the mind into impressions and ideas, will draw skeptical conclusions from similar premises. Kant will attempt to rescue the external world by distinguishing phenomena from things in themselves.

Hume divides "all the perceptions of the mind into two classes or species, which are distinguished by their different degrees of force or vivacity. The less forcible and lively are commonly denominated Thoughts or Ideas. The other species want a name in our language and in most others . . . Let us, therefore, use a little freedom and call them Impressions." By this term, Hume explains, "I mean all our more lively perceptions, when we hear, or see, or feel, or love, or hate, or desire, or will." Every simple idea is a copy of a corresponding simple impression, and the difference between them is one of degree rather than of kind.

This distinction serves as a criterion for the reality of ideas. Any supposed idea that cannot be traced back to an originating impression is empty, a word without genuine content. The idea of substance, the idea of necessary connection between cause and effect, and the idea of a self that persists through time are all subjected to this test and found wanting. There is no impression of causal necessity, only the experience of one event regularly following another and the mind's habit of expecting the sequence to continue. The self, investigated carefully, is "nothing but a bundle or collection of different perceptions." The question of the reality of ideas, and of the criteria by which real ideas are distinguished from fantasies and fictions, is treated also under the idea of Truth.

Hume also acknowledges that ideas as well as impressions are involved in our knowledge of matters of fact, but "relations between ideas may also be objects of knowledge, as in the sciences of geometry, algebra, and arithmetic." The distinction between knowledge of matters of fact and knowledge of the relations among ideas is central to Hume's epistemology. Complex ideas are assembled by combining simple ideas, but every component must have its origin in experience. The association of ideas in the stream of thought by relationships of contiguity, succession, and resemblance is one of the basic facts of mental life that Hume describes.

Kant credits Hume with awakening him from "dogmatic slumber" and reconstructs the theory of ideas from the ground up, distinguishing between intuitions given by sensibility, concepts produced by the understanding, and ideas generated by reason that reach beyond all possible experience.

Kant distinguishes three levels of representation: intuitions, given by sensibility; concepts, produced by the understanding and applicable to experience; and ideas, generated by reason, reaching beyond all possible experience. "I understand by idea," Kant writes, "a necessary concept of reason to which no corresponding object can be given in sense-experience." He acknowledges his debt to Plato, observing that "Plato made use of the expression 'idea' in such a way as quite evidently to have meant by it something which not only can never be borrowed from the senses but far surpasses even the concepts of the understanding."

Precisely because ideas outstrip experience, they cannot yield knowledge in the strict sense. When reason tries to use them as if they described actual objects, it falls into antinomies, equally valid proofs that the world is and is not infinite, that freedom does and does not exist, and paralogisms, invalid inferences about the nature of the soul. These illusions are not accidental errors but structural features of reason overstepping its bounds. The Transcendental Dialectic is a systematic diagnosis of where reason goes wrong when it mistakes its own regulative principles for descriptions of objects. The derivation of transcendental ideas from the three syllogisms of reason is one of the most technical aspects of Kant's analysis, treated also under the idea of Reasoning.

Yet ideas are not without function. They serve a regulative purpose: they guide inquiry by directing us to seek ever greater systematicity and completeness in our knowledge, even though the totality they point toward can never be given in experience. "Reason cannot permit the systematic unity of its cognitions to be regarded as merely contingent; it prescribes this unity as a task." We pursue science as if the world formed a complete rational system; we treat agents as if they were free; we speak of God as if all natural purposes converged on an intelligent design. These stances organize inquiry without claiming to describe things in themselves. Kant thus preserves something of Plato's reverence for ideas while denying that we can know the realities they purport to represent.

Kant's treatment of ideas closes the early modern debate and opens the post-Kantian one. The word "idea" has traveled from Plato's eternal Forms, through Descartes' innate contents, Locke's sensory deliverances, and Hume's faint copies, to arrive at the necessary concepts of a bounded reason. The various theories of idea thus range from those which identify an idea with a sensation or perception to those which deny any relationship between ideas and the elements of sense, and the issues raised by these conflicting analyses remain among the most fundamental in the tradition.