Early in the 20th Century, the British philosopher G. E. Moore noticed that sentences of a certain form have a quite peculiar feature. Consider:
I believe it is Tuesday, but today is Monday.
Today is Monday, but I do not believe that.
I believe that today is Tuesday, but it’s not true that today is Tuesday.
These statements, when considered as first-personal assessments, instantiate what’s been called Moore’s Paradox. Taking ‘p’ as a variable standing for any well-formed declarative sentence, we can say that Moore’s Paradox is generated by any statement of the following form,
I believe that p, but not-p.
What is peculiar about statements of this kind is that although they may be true, you cannot believe them to be true in your own case. Although you may, indeed, be mistaken about what day today is, you cannot assess yourself as being mistaken about the day without undoing your belief about what day today is. When we assess one of our beliefs as false, we typically thereby dissolve the belief. Put otherwise, there are some truths that cannot be believed. That’s the paradox.
What are we to make of this? Philosophers have proposed various accounts of the significance of Moore’s Paradox. One clear implication is that beliefs are intrinsically truth-aiming. When one believes, one aims to believe what is true. This is why falsity is a decisive objection to a belief. When one finds oneself driven to affirm something that one regards as false, the language of belief no longer seems appropriate; one instead employs diagnostic terms, such as affliction, addiction, and delusion. We may say, then, that truth is the norm of belief.