Certainty

‘Certainty’ is not a univocal term. It is predicated of people, and it is predicated of propositions. When certainty is predicated of a person, as in ‘Sally is certain that she parked her car in lot 359’, we are ascribing an attitude to Sally. We can say that a person, S, is psychologically certain of a proposition, p, just in case S believes p without any doubts. In general, psychological certainty has not been a topic which philosophers have found problematic.

On the other hand, certainty as a property of propositions, as in ‘The proposition that Sally parked her car in lot 359 is certain for Sally’, has been discussed widely by philosophers. Roughly, we can say that a proposition, p, is propositionally certain for a person, S, just in case S is fully warranted in believing that p and there are no legitimate grounds whatsoever to doubt that p. The philosophical issue, of course, is whether there are any such propositions and, if so, what makes them certain.