What is a Truism?
For some object O and proposition p, Suppose it is true that:
(1) P is a truism about O.
There are several ways to interpret (1). Here's a really weak way:
[WEAK]: P is true about O.
But this is surely too weak. Lots of propositions might be true about O and aren't such that we would say they are "truisms" about O.
How about something stronger:
[STRONG]: P is true about O, and is true about O in most nearby worlds in which O holds.
Hmm... maybe? This seems plausible, but it's not obvious.
What about something even stronger:
[SUPERSTRONG]: P is constitutive of the concept of O.
For example, that a bachelor is unmarried is constiutive of the concept of a bachelor, and is also surely a 'truism' about bachelors (if anything is a truism about anything.) Does "A bachelor is unmarried" just happen to be both a truism about bachelors and constitutive of the concept of bachelor? This is tricky. It seems as though it 's more than coincidence. However, we should probably be careful before endorsing 'superstrong' as something that follows from the claim that p is a truism about O. Consider that other plausible candidates for 'truisms' don't admit of such strong conceptual inferences. Consider:
(2) "What goes up must come down" is a truism about what goes up. If you think there is such a thing as a truism, you'd be hard pressed to claim that (2) isn't a truism; at least, you'd certainly fly in the face of the folk-approved norms that govern the use of truism.
But if (2) is a truism, then Superstrong is false. That something must come down is not constitutive of the concept of "goes up" or "ascends".
So what the heck is a truism???