For every descriptive statement that we make, we have to decide whether the truth-value of the proposition we wish to express is true or false, or, whether we wish to express that its truth-value is not fully known to us. We express – in our view – true propositions by affirmative sentences and false propositions by negative sentences, where ‘negative’ means that the sentence contains some overt negative element (e.g. not). Uncertain truth-values can be expressed by adverbials like probably, likely, certainly, etc., but in this chapter we will not be concerned with these. In English, as in the vast majority of other languages, affirmative sentences receive no special marking, while negative sentences are typically marked by one or more negative expressions. Apparently, we consider the making of positive statements the norm, and verbally express the absence of a positive truth-value.

Strictly speaking, the assignment of clear truth-values is only possible for what is known in the relevant literature as ‘constative utterances’ (Austin 1962; Searle 1969). These are, by and large, descriptive statements that contrast with performative utterances of the type ‘I hereby christen this child “John”.’, i.e. utterances used for effectuating a change in the state in which the world is. Such utterances cannot be assigned a truth-value, as they require certain felicity conditions for their successful application. Some performative utterances, like the one just mentioned, are clearly odd when negated, but this should not be taken to mean that such utterances cannot in general be negated (Don't move!, I do not apologise., etc.).