In logic, a proposition may be a truism even if it is not a tautology, a restatement of a definition, or a theorem derived from axioms that are generally held to be true. In fact, some would say that such analytic propositions should not be regarded as truisms.
In philosophy, a sentence which asserts incomplete truth conditions for a proposition may be regarded as a truism. An example of such a sentence would be: "Under appropriate conditions, the sun rises." Without contextual support — a statement of what those appropriate conditions are — the sentence is true but uncontestable. A statement which is true by definition ("All cats are mammals.") would also be considered a truism.
Often the word is used to disguise the fact that a proposition is really just a half-truth or an opinion, especially in rhetoric.
It's a truism that in hard economic times people seek escapist art and entertainment. During the American Depression of the 1930s, cinema audiences liked nothing better than to watch Fred Astaire and Ginger Rogers tap dancing their way through the swanky resorts of Europe and to weep with Nelson Eddy and Jeanette MacDonald as they warbled their undying love for each other in some idealised Heidelberg.
Apr 18, 2009; It's a Truism that in hard economic times people seek escapist art and entertainment. During the American Depression of...