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.

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 contentless.

Often the word is used to disguise the fact that a proposition is really just a half-truth or an opinion, especially in rhetoric.

Examples

• In logic: "A AND NOT A is a contradiction".
• In set theory: a branch of abstract mathematics, "the intersection of a set and its complement is the null set".
• In English: "It's a truism that prevention is better than cure."

See also

• tautology
• contradiction
• synthetic proposition
• aphorism
• axiom
• banality
• cliché
• commonplace
• dictum
• fact
• gospel
• maxim
• moral
• Jacques de La Palice