from The American Heritage® Dictionary of the English Language, 5th Edition.

  • noun A set of statements or principles devised to explain a group of facts or phenomena, especially one that has been repeatedly tested or is widely accepted and can be used to make predictions about natural phenomena.
  • noun The branch of a science or art consisting of its explanatory statements, accepted principles, and methods of analysis, as opposed to practice.
  • noun A set of theorems that constitute a systematic view of a branch of mathematics.
  • noun Abstract reasoning; speculation.
  • noun A belief or principle that guides action or assists comprehension or judgment.
  • noun An assumption based on limited information or knowledge; a conjecture.

from The Century Dictionary.

  • noun Contemplation.
  • noun Perception or consideration of the relations of the parts of an ideal construction, which is supposed to render completely or in some measure intelligible a fact or thing which it resembles or to which it is analogous; also, the ideal construction itself.
  • noun An intelligible conception or account of how something has been brought about or should be done.
  • noun Plan or system; scheme; method.
  • noun In mathematics, a series of results belonging to one subject and going far toward giving a unitary and luminous view of that subject: as, the theory of functions.
  • noun Specifically, in music, the science of composition, as distinguished from practice, the art of performance.
  • noun At this point we may again for a moment turn aside to consider the so-called Conscious Automaton Theory.

from the GNU version of the Collaborative International Dictionary of English.

  • noun A doctrine, or scheme of things, which terminates in speculation or contemplation, without a view to practice; hypothesis; speculation.
  • noun An exposition of the general or abstract principles of any science.
  • noun The science, as distinguished from the art.
  • noun The philosophical explanation of phenomena, either physical or moral
  • noun etc. See under Atomic, Binary, etc.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

  • noun countable (logic) A set of axioms together with all statements derivable from them. Equivalently, a formal language plus a set of axioms (from which can then be derived theorems).

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • noun a belief that can guide behavior
  • noun a well-substantiated explanation of some aspect of the natural world; an organized system of accepted knowledge that applies in a variety of circumstances to explain a specific set of phenomena
  • noun a tentative insight into the natural world; a concept that is not yet verified but that if true would explain certain facts or phenomena


from The American Heritage® Dictionary of the English Language, 4th Edition

[Late Latin theōria, from Greek theōriā, from theōros, spectator : probably theā, a viewing + -oros, seeing (from horān, to see).]

from Wiktionary, Creative Commons Attribution/Share-Alike License

From Late Latin theōria, from Ancient Greek θεωρία (theōria, "contemplation, speculation, a looking at, things looked at"), from θεωρέω (theōreō, "I look at, view, consider, examine"), from θεωρός (theōros, "spectator"), from θέα (thea, "a view") + ὁράω (horaō, "I see,look").


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  • I must be a dinosaur too--maybe even more of one, because I have a similar problem even with articles that purport to be about a piece of literature but are really about theory--and only use literature to prove the *theory* correct.

    A Question of Philosophy: Grad School Theater Heo 2006

  • Thermodynamic laws are unified with mechanical theory through an *application of information theory*.

    It’s A Big Deal in Kansas « UDreamOfJanie 2006

  • This theory, it should be remembered, is _merely a theory_, _a mere notion_, _a hypothesis_.

    Fables of Infidelity and Facts of Faith Being an Examination of the Evidences of Infidelity Robert Patterson 1857

  • But _your_ theory is _theory_ in the worst sense of the word.

    Sophisms of the Protectionists Fr��d��ric Bastiat 1825

  • Now that we have sufficient evidence from the authorities that carbonic acid can be retained in the blood by excessive breathing, and enough to seriously affect the brain, and what its effects are when taken directly into the lungs in excess, we can enter upon what I have held as the most reasonable theory of the phenomenon produced by rapid breathing for analgesic purposes; which _theory_ was not _first_ conceived and the process made to yield to it, but the phenomenon was long observed, and from the repetition of the effects and their close relationship to that of carbonic acid on the economy, with the many experiments performed upon myself, I am convinced that what I shall now state will be found to substantiate my discovery.

    Scientific American Supplement, No. 275, April 9, 1881 Various

  • Anyway, I wasn’t comparing EW theory or QCD to string theory; I was comparing * gauge theory*, in complete generality, to string theory.

    String Theory is Losing the Public Debate Sean 2007

  • I didn’t say an assumption was a theory; I guess someone who can read “Anomaly is simply defined as a period of more than 50 yr of sustained warmth, wetness or dryness, within the stipulated interval ” as meaning ‘warmth, whether wet or dry’ and EXCLUDING consideration of moisture, can also read “The assumption of invariant conditions is a falsifiable assumption embedded within dendrochronological **theory**,” as meaning that ‘assumption’ is synonymous with ‘theory.’

    Treydte, Moberg, Soon and Baliunas « Climate Audit 2006

  • Any of these doubters like to say that evolution is “only a theory,” not realizing that, in science, the term theory has a very specific meaning and implies a large amount of supporting evidence as you recently explained in your column.

    The Right Word in the Right Place at the Right Time William Safire 2004

  • Any of these doubters like to say that evolution is “only a theory,” not realizing that, in science, the term theory has a very specific meaning and implies a large amount of supporting evidence as you recently explained in your column.

    The Right Word in the Right Place at the Right Time William Safire 2004

  • It is also a theory and when people understand how sciences use the term theory, which is more important than facts.

    Crimson White RSS 2009


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  • You have brought us all this way to show us a French triangle. Do you believe your own theory?

    -- No, Stephen said promptly.

    Joyce, Ulysses, 9

    January 6, 2007

  • An ounce of action is worth a ton of theory.

    -Friedrich Engels

    October 19, 2008

  • Evolution is just a...

    March 8, 2009

  • If you are skeptical by nature, unfamiliar with the terminology of science, and unaware of the overwhelming evidence, you might even be tempted to say that it's "just" a theory. In the same sense, relativity as described by Albert Einstein is "just" a theory. The notion that Earth orbits around the sun rather than vice versa, offered by Copernicus in 1543, is a theory. Continental drift is a theory. The existence, structure, and dynamics of atoms? Atomic theory. Even electricity is a theoretical construct, involving electrons, which are tiny units of charged mass that no one has ever seen. ... That's what scientists mean when they talk about a theory: not a dreamy and unreliable speculation, but an explanatory statement that fits the evidence.

    (David Quammen, on National Geographic)

    March 8, 2009