This paper attempts to outline a model for the semantic interpretation of mood and modality in constructions of knowledge or belief, as realized in the finite verb in English. It does so in terms of the attitude(s) which the speaker is seen as presenting him/herself to hold towards the proposition expressed in the clause. The account of such attitudes is based on an epistemic logic, extended to take probabilities into account, and is presented in terms of set theory. The approach takes epistemic mood to be realized either by marking (overt or covert) on the stem of the lexical verb or by the choice of an auxiliary verb. Semantic distinctions between different modal auxiliaries of knowledge/belief are analysed in the same terms as the contrast between the epistemic subjunctive and indicative moods of the finite full verb. One effect of this approach is that the semantics of epistemic mood and epistemic modality is treated as an integrated continuum. Some benefits are claimed to derive from this approach in the conclusion, including that of establishing different types, as well as degrees, of certainty.