Definition Of theory
a supposition or a system of ideas intended to explain something, especially one based on general principles independent of the thing to be explained.
Darwin's theory of evolution
Example Of theory
a theory of education
A simple theoretical construct underlies the theory and practice of counterinsurgency warfare.
And of course my personal theory on this is that women, who do childbirth after all, can handle a lot more pain.
And of course there is the theory that the dinosaurs were wiped out by a mega-tsunami caused by an asteroid.
And of course, as the theory of nuclear deterrence ordains, India and Pakistan, being nuclear powers, would never go to war again.