Abstract

This paper presents and discusses Henri Poincaré’s view on the logical non-derivability of imperatives from indicatives. Firstly, his point of view is compared with David Hume’s. Then Poincaré’s thesis is shown to have been implicitly or explicitly essential to attempts to build a logic of imperatives (norms) as a special linguistic category as well as a deontic logic. The paper shows deontic logic enables us to formulate general principles concerning the logical separability of deonticals (sentences with deontic operators) and non-deontic sentences. Finally, the paper includes remarks on the reception of Poincaré’s discussed ideas in later logical and philosophical literature with the second issue illustrated by legal philosophy.