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 a falsism.
[1] In philosophy, a sentence which asserts incomplete truth conditions for a proposition may be regarded as a truism.
[2] 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.
[3] Lapalissades, such as "If he were not dead, he would still be alive", are considered to be truisms.