A Paradox or a Contradiction?
I’ve seen versions of this claim on social media. I don’t know who the source is. Let’s focus on the claim itself. It is paradoxical, if not contradictory.
“Stupidity is knowing the truth yet not believing it.”
Now, it is a matter of broad agreement among philosophers that (propositional) knowledge is at least a matter of justified true belief (JTB). In other words, for a person S to know some proposition p, the following conditions are necessary, even if not sufficient:
p is true.
S believes that p.
p is justified for S (i.e., S believes that p based on adequate reason).
Condition (2) is that knowledge requires belief. If this is correct, then it is impossible to know something yet not believe it. But the statement in quotation marks above holds that it is possible to know something and yet not believe it, although to do so is a mark of stupidity.
How can knowing something involve not believing it? It would seem that a lack of belief entails a lack of knowledge. And yet there are strange cases in which people seem to know that, say, they will lose the lottery or that they are not really what they purport themselves to be, and yet in some sense, they believe that they will win the lottery or that they are what they purport themselves to be.