a coherent group of tested general propositions, commonly regarded as correct, that can be used as principles of explanation and prediction for a class of phenomena: Einstein's theory of relativity.
a proposed explanation whose status is still conjectural and subject to experimentation, in contrast to well-established propositions that are regarded as reporting matters of actual fact.
Mathematics. a body of principles, theorems, or the like, belonging to one subject: number theory.
the branch of a science or art that deals with its principles or methods, as distinguished from its practice: music theory.
a particular conception or view of something to be done or of the method of doing it; a system of rules or principles: conflicting theories of how children best learn to read.
contemplation or speculation: the theory that there is life on other planets.
guess or conjecture: My theory is that he never stops to think words have consequences.
Idioms about theory
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
How to use theory in a sentence
But privately, it is listening to other theories, including those about an inside job.FBI Won’t Stop Blaming North Korea for Sony Hack -- Despite New Evidence | Shane Harris | December 30, 2014 | THE DAILY BEAST
That plane still has not been found, sparking much speculation and many conspiracy theories.The Presumed Crash of AirAsia Flight QZ8501 Is Nothing Like MH370 | Lennox Samuels | December 29, 2014 | THE DAILY BEAST
But his motives for shooting John Paul II have remained a mystery shrouded in multiple conspiracy theories.
Instead, they spin dark theories that it was all a set-up to make Pakistan look bad.Pakistan’s Dance With Terrorists Just Backfired and Killed 132 Children | Chris Allbritton | December 17, 2014 | THE DAILY BEAST
He acknowledged the theories but his voice lacked conviction.Alfred Hitchcock’s Fade to Black: The Great Director’s Final Days | David Freeman | December 13, 2014 | THE DAILY BEAST
Moreover, the Bible teaches erroneous theories of history, theology, and science.
To escape from these horrible theories, the Christians (some of them) have thrown over the doctrines of Hell and the Devil.
But the best of theories do not always stand the test of practice and so it was found in this case.Fifty Years of Railway Life in England, Scotland and Ireland | Joseph Tatlow
It has upheld the grossest errors and the most fiendish theories as the special revelations of God.
Blood must always tell in England—although in America—if Mrs. Hofer is a type—well, this is the land of reversed theories.Ancestors | Gertrude Atherton
British Dictionary definitions for theory
a system of rules, procedures, and assumptions used to produce a result
abstract knowledge or reasoning
a speculative or conjectural view or idea: I have a theory about that
an ideal or hypothetical situation (esp in the phrase in theory)
a set of hypotheses related by logical or mathematical arguments to explain and predict a wide variety of connected phenomena in general terms: the theory of relativity
a nontechnical name for hypothesis (def. 1)
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
Scientific definitions for theory
A set of statements or principles devised to explain a group of facts or phenomena. Most theories that are accepted by scientists have been repeatedly tested by experiments and can be used to make predictions about natural phenomena. See Note at hypothesis.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Cultural definitions for theory
The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.