In the early 1930s, the Polish philosopher and logician Kazimierz Ajdukiewicz (1890–1963) proposed a new formal approach to natural language which, unlike Chomsky’s, was based on a joint calculus of the grammaticality and meaning of sentences. This methodological choice, which resulted from Ajdukiewicz’s reflections on the nature of language, led him to consider different conceptions of meaning implementable in a syntactical algorithm. The aim of this paper is to retrace the various solutions provided by Ajdukiewicz to meet this challenge that will continue to be a real issue for future categorial grammars.