Origin: Latin suffix -ory
Theory has 4 different meanings across 1 category:
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
"theories can incorporate facts and laws and tested hypotheses"
"true in fact and theory"
a tentative insight into the natural world; a concept that is not yet verified but that if true would explain certain facts or phenomena
"a scientific hypothesis that survives experimental testing becomes a scientific theory"
"he proposed a fresh theory of alkalis that later was accepted in chemical practices"
a belief that can guide behavior
"the architect has a theory that more is less"
"they killed him on the theory that dead men tell no tales"
A description of an event or system that is considered to be accurate.
"The new climate theory accurately predicts rising sea levels based on decades of ocean data."
In plain English: A theory is an educated guess about how something works based on evidence and reasoning.
"The teacher asked if anyone had a theory about why the experiment failed."
Usage: Use theory when referring to a well-substantiated explanation of some aspect of the natural world, such as gravity or evolution, rather than just a guess or unproven idea. Distinguish it from "hypothesis," which describes an initial assumption made before sufficient evidence exists to confirm its accuracy.
The word theory comes from the Ancient Greek θεωρία, which originally meant "contemplation" or "a looking at." It entered English via Middle French and Late Latin, carrying its sense of observing or examining something carefully.