“Certain” represents an assessment of the evidence for a conclusion; it is
usually contrasted with two other broad types of assessment: “possible” and
“probable.” . . .
Idea X is “certain” if, in a given context of knowledge, the evidence for X is
conclusive. In such a context, all the evidence supports X and there is no
evidence to support any alternative . . . .
You cannot challenge a claim to certainty by means of an arbitrary
declaration of a counter-possibility, . . . you cannot manufacture
possibilities without evidence . . . .
All the main attacks on certainty depend on evading its contextual character . . . .
The alternative is not to feign omniscience, erecting every discovery into an
out-of-context absolute, or to embrace skepticism and claim that knowledge is
impossible. Both these policies accept omniscience as the standard: the
dogmatists pretend to have it, the skeptics bemoan their lack of it. The
rational policy is to discard the very notion of omniscience. Knowledge is
contextual—it is knowledge, it is valid, contextually.