theory

/ˈθɪri/
noun
  1. A formal set of ideas that explains something, based on general principles and supported by evidence.
    • In science class, we learned about the theory of plate tectonics.
    • The theory of evolution explains how species change over time.
    • Einstein's theory of relativity changed physics forever.
  2. An idea or opinion that someone has, especially one that is not proven.
    • I have a theory about why the cookies disappeared so fast.
    • He has a theory that eating chocolate makes you smarter.
    • Her theory is that the dog hid the toy under the couch.
  3. The general principles or ideas of a subject, rather than the practical skills of doing it.
    • In theory, this plan should work, but in practice it might be hard.
    • The course covers both music theory and playing an instrument.
    • You need to learn the theory before you can drive a car.
Antonyms
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