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.

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.

Lapalissades, such as "If he were not dead, he would still be alive", also considered to be truisms.

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