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theory

n.
US //ˈθiɝi// UK //θˈiəɹi// the·o·ry
  1. 1 scientific explanation (n.)
    B2 Upper Intermediate Academic Science

    a well-tested explanation that uses facts to show how a part of the natural world works.

    a coherent set of propositions used as principles of explanation for a class of phenomena, typically confirmed through observation or experiment.

    Example

    In school, we studied the theory of evolution and how species change over time.

    Example

    The general theory of relativity fundamentally altered our understanding of space, time, and gravity within the physical sciences.

    Usage

    Often used with 'of' followed by the subject of study.
  2. 2 principles vs practice (n.)
    B2 Upper Intermediate Academic

    the rules and ideas of a subject, rather than the actual doing of it.

    the body of rules, ideas, and principles of a particular subject or skill as distinguished from its practical application.

    Example

    The course covers both music theory and how to play the piano.

    Example

    While the candidate understood the theory of management, he struggled with the practical realities of leading a large team.
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  1. 3 an idea or guess (n.)
    B1 Intermediate Informal

    an idea that someone has to explain something, even if it is not proven yet.

    a hypothesis, conjecture, or individual opinion offered as an explanation for an event.

    Example

    I have a theory that the cat only meows when she wants treats.

    Example

    Detectives are working on a theory that the two robberies were committed by the same group of people.

    Teacher's tip

    In casual conversation, 'theory' is often used where a scientist would prefer 'hypothesis' or 'guess'.
  2. 4 mathematical logic (n.)
    C1 Advanced Technical Academic Math

    a set of rules and statements that are logically connected to each other.

    a set of axioms and all the statements that can be logically derived from them within a formal system.

    Example

    The professor explained how set theory forms the basis of modern mathematics.

    Example

    In model theory, we investigate the relationship between formal languages and their interpretations in various mathematical structures.
    • formal system
    • axiomatization
Origin

From Middle French théorie, from Late Latin theōria, from Ancient Greek θεωρία (theōría, “contemplation, divine perspective, speculation, a looking at, a seeking”), from θεωρέω (theōréō, “I look at, view, see, consider, examine”), from θεωρός (theōrós, “spectator”), from θέα (théa, “view, perspective, sight”) + ὁράω (horáō, “I see, look”) [i. e. θέαν ὁράω (théan horáō, “see, look at a view; survey + genitive”)].

Word family

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