This study analyses the semantics of English deontic adjectives like essential and appropriate, and uses this to refine traditional definitions of deontic modality, which are mainly based on the study of modal verbs. In a first step, it is shown that the set of meanings associated with deontic adjectives is quite different from the set of meanings identified in the literature on modal verbs. Adjectives lack the directive meanings of obligation or permission, which are traditionally regarded as the core deontic categories, and they have semantic extensions towards non-modal meanings in the evaluative domain. In a second step, the analysis of adjectives is used to propose an alternative definition of deontic modality, which covers both the meanings of verbs and adjectives, and which can deal with the different extensions towards modal and non-modal categories. This is integrated into a conceptual map, which works both in diachronydefining pathways of change -and in synchrony -accommodating refinements within each set of meanings.