An idea (Greek: ιδέα) is a specific thought or concept that arises in the mind of a person as a result of thinking. The term arises in both popular and philosophical terminology.

The colloquial expression "I have no idea" may be used in any situation where the speaker is ignorant of something. In this general sense the term is synonymous with "concept".



The view that ideas exist in a realm separate or distinct from real life is a venerable theme in philosophy. This view holds that we only "discover" ideas in the same way that we discover the real world.

In philosophy, the term “idea” is common to all languages and periods, but there is scarcely any term which has been used with so many different shades of meaning.


  • Plato utilized the concept of idea in the realm of metaphysics. He asserted that there is realm of Forms or Ideas, of which things in the world are mere imperfect reflections or instantiations.

John Locke

  • In striking contrast to Plato’s use of idea is that of John Locke, who defines “idea” as “whatever is the object of understanding when a man thinks” (Essay on the Human Understanding (I.), vi. 8). Here the term is applied not to the mental process, but to anything whether physical or intellectual which is the object of it.

David Hume

  • Hume differs from Locke by limiting “idea” to the more or less vague mental reconstructions of perceptions, the perceptual process being described as an “impression.”

Wilhelm Wundt

  • Wundt widens the term to include “conscious representation of some object or process of the external world.” In so doing, he includes not only ideas of memory and imagination, but also perceptual processes, whereas other psychologists confine the term to the first two groups.

G. F. Stout & J. M. Baldwin

  • G. F. Stout & J. M. Baldwin, in the Dictionary of Philosophy and Psychology, define “idea“ as “the reproduction with a more or less adequate image, of an object not actually present to the senses.” They point out that an idea and a perception are by various authorities contrasted in various ways. “Difference in degree of intensity,” “comparative absence of bodily movement on the part of the subject,” “comparative dependence on mental activity,” are suggested by psychologists as characteristic of an idea as compared with a perception.

It should be observed that an idea, in the narrower and generally accepted sense of a mental reproduction, is frequently composite. That is, as in the example given above of the idea of chair, a great many objects, differing materially in detail, all call a single idea. When a man, for example, has obtained an idea of chairs in general by comparison with which he can say “This is a chair, that is a stool,” he has what is known as an “abstract idea” distinct from the reproduction in his mind of any particular chair (see abstraction). Furthermore a complex idea may not have any corresponding physical object, though its particular constituent elements may severally be the reproductions of actual perceptions. Thus the idea of a centaur is a complex mental picture composed of the ideas of man and horse, that of a mermaid of a woman and a fish.

In anthropology and the social sciences

Diffusion studies explore the spread of ideas from culture to culture. Some anthropological theories hold that all cultures imitate ideas from one or a few original cultures, the Adam of the Bible or several cultural circles that overlap. Evolutionary diffusion theory holds that cultures are influenced by one another, but that similar ideas can be developed in isolation.

In mid-20th century, social scientists began to study how and why ideas spread from one person or culture to another. Everett Rogers pioneered diffusion of innovations studies, using research to prove factors in adoption and profiles of adopters of ideas.

Ideas as property

Main article: intellectual property

In some cases the manner in which certain ideas are expressed can be granted legal protection by the state as intellectual property. Intellectual property laws generally do not give any protection to the actual idea which forms the basis of the intellectual property. Such laws do not bestow the legal status of property upon ideas per se. Instead, it is the fundamental expression of the idea which is protected by a variety of different intellectual property laws. The relevant law depends on the subject matter, such as copyright in the case of an original literary work, a patent grant in the case of an invention, a registered trademark in the case of a brand name, or registered industrial design rights in the case of the physical appearance of certain objects.

Patent law protects a new idea that has a functional manifestation as invention or know-how, copyright law protects the expression of ideas like books, movies, videodiscs, and datastreams, while other laws protect industrial designs and integrated circuit patterns. Those types of law are intended to protect the exploitation of the expression of the ideas of creators and authors for a limited period of time in a form of monopoly.

Related topics

Further reading

  • Peter Watson (2005), Ideas: a history from fire to Freud, Weidenfeld & Nicholson


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