Definition of "theory"

As they encrease the hatred of vice in some, so doe they enlarge the theory of wickednesse in all.

1646, Thomas Browne, Pseudodoxia Epidemica, VII.19

In its most proper acceptation, theory means the completed result of philosophical induction from experience.

1843, John Stuart Mill, ""A System of Logic, Ratiocinative and Inductive, ..., Bk V, Ch 7

Does this mean, then, that there can be no such thing as a theory of literature?

1990, Tony Bennett, Outside Literature, page 139

It was only when Einstein's theory of relativity was published in 1915 that physicists could show that Mercury's "anomaly" was actually because Newton's gravitational theory was incomplete.

2002 May 23, Duncan Steel, The Guardian

The world would need additional decades [...] before the Big Bang would begin to move from interesting idea to established theory.

2003, Bill Bryson, A Short History of Nearly Everything, BCA, page 118

Scientists and creationists are understanding the word "theory" in two very different senses. Evolution is a theory in the same sense as the heliocentric theory. In neither case should the word "only" be used, as in "only a theory".

2009, Richard Dawkins, The Greatest Show On Earth: The Evidence for Evolution, Bantam, page 10

Some of the most beautiful and thus appealing physical theories, including quantum electrodynamics and quantum gravity, have been dogged for decades by infinities that erupt when theorists try to prod their calculations into new domains. Getting rid of these nagging infinities has probably occupied far more effort than was spent in originating the theories.

2012 January, Michael Riordan, “Tackling Infinity”, in American Scientist‎, volume 100, number 1, archived from the original on 30 April 2013, page 86

Lopukhov wrote a number of books and articles on ballet theory, as well as his memoirs.

1998, Elizabeth Souritz, The Great History of Russian Ballet

It's just a theory I have, and I wonder if women would agree. But don't men say a lot about themselves when a short-skirted woman slides out of a car or chair?

1999, Wes DeMott, Vapors

The theory is that by stripping costs to the bone, they are able to offer ludicrously low fares.

2003 June 21, Sean Coughlan, The Guardian