The paper presents results of a corpus-based study of basic means used to express strong deontic necessity not to in English and their counterparts in Czech. In particular, by means of co-text analysis, different semantic values of these means of expression are delimited. It is further studied to what extent the choice of particular means is influenced by co-occurring means at different levels: grammatical (colligations), pragmatic as well as by the type of discourse. The matter is first studied within one language and then the structures of semantic field of necessity not to in English and Czech are compared.