The judgments about which we're morally certain aren't universally regarded as true. So judgments of this kind lack any objective criterion that would allow us to decide at once whether they're true or false. Such a criterion exists for the other two kinds of certainty; but with moral certainty, there's simply no objective sign, and this accounts for the diversity of opinion.

What explains the certainty we feel in these cases? It can't be purely logical, for when we're morally certain, we feel no need to prove logically – to ourselves or others – the judgments we affirm. Were we to draw up a list – as complete as possible – of the purely logical considerations that go into an architect's plans, we'd see that these bear no relation to the strength of the architect's conviction. The same would be true of the purely logical motives we might list for some of our political or religious opinions. We would see a huge gap between their value and our certainty. With moral certainty, therefore, we must acknowledge the intervention of nonlogical psychological elements. In fact, intelligence often acts together with will and sensibility, so it's not surprising that these faculties influence our certainty. Our sensibility has a more or less vague affinity with one side or the other in a dispute, which is explained by our temperament, education, habits, and heredity.