Based on a functional approach, the article proposes a role for lexical knowledge in human languages in relation to syntactic and encyclopaedic knowledge. A lexicon presupposes encyclopaedic knowledge in terms of which the semantic domain of lexical items can be defined – but this does not mean that there is no distinction between lexicon and encyclopaedia, only that one stands on the shoulders of the other. Syntax similarly presupposes a lexicon: there can be no combinations without items to be combined, whereas you can have (holophrastic) languages consisting solely of items. However, inside the domain of human, i.e. syntactically organized languages, syntax and lexicon presuppose each other: lexical items below full utterance size make no sense except in relation to a combinatory syntax, and a combinatory syntax presupposes elements that can enter into combinations.