Contrary to what some people believe, the word truism is not a more elegant word for truth. While the word truth can occasionally be used to refer to a “truism,” since truisms are often true, the reverse—the use of truism to mean “truth”—is unwise. Truism stands for a certain kind of truth—a cliché, a platitude, something so self-evident that it is hardly worth mentioning. One can use it to accuse another writer or speaker of saying something so obvious or evident and trite that pointing it out is pointless. To say that a statement is a truism when you intend to compliment it as truthful, factual, even provable, will merely serve to confuse those who know that calling something a truism is not praise, but a criticism or insult.
Note, however, that truism is used in a technical sense in mathematics or philosophy for restating something that is already known from its terms or premises. Examples of such truisms include: “Men are not women” and “Since the circumference of a circle equals twice the radius multiplied by π (2πr), it equals the diameter multiplied by π (πd).”