 The difficulty for this conception of certainty is specifying the precise sense in which the belief could not have been false. What is meant cannot be what is called metaphysical or broadly logical impossibility. Although some of the paradigmatically certain beliefs are necessarily true in this sense, many others are not. For example, though I am certain of the truth of the cogito, it is not necessarily true (in the metaphysical sense) that I exist. That is, it is possible that I might not have existed. We might attempt to solve this difficulty by saying that the belief is guaranteed to be true by the subject’s grounds for it (see, e.g., Audi 1998, pp. 218–9). But this opens up two further problems for this conception of certainty. First, if the truth of the belief is guaranteed by the subject’s grounds for holding it, then it looks as though the certainty of the belief ought to be attributed to those grounds as well. That is to say, the belief would be certain, not in virtue of the fact that it is guaranteed to be true, but rather in virtue of its relation to the grounds that make that guarantee possible. This would be so because the grounds would provide a deeper explanation for the certainty of the belief than would the fact that the belief is guaranteed to be true. Moreover, some further account of the certainty of the grounds will still need to be provided.