A truism is a claim that is so obvious or self-evident as to be hardly worth mentioning, except as a reminder or as a rhetorical or literary device and is the opposite of falsism.[1]
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".[2]
The word may be used to disguise the fact that a proposition is really just an opinion, especially in rhetoric. A saying about people or an accepted truth about life in general is also a truism.