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 incontestable. A statement which is true by definition ("All cats are mammals.") would also be considered a truism. This is quite similar to a tautology in which the conclusion of a statement is essentially equivalent to its premise, a statement that is "true by virtue of its logical form alone".
The word may be used to disguise the fact that a proposition is really just an opinion, especially in rhetoric. Stating an accepted truth about life in general can also be called a truism.
See also 
- "Definition: truism". http://www.websters-online-dictionary.org/: Webster's Online Dictionary. Retrieved 2010-03-10. "Noun Base (truism)