This article proposes a new way of understanding grammatical status and grammaticalization as distinctive types of linguistic phenomena. The approach is usage-based and links up structural and functional, as well as synchronic and diachronic aspects of the issue. The proposal brings a range of hitherto disparate phenomena into a motivated relationship, while certain well-entrenched criteria (such as ‘closed paradigms’) are shown to be incidental to grammatical status and grammaticalization. The central idea is that grammar is constituted by expressions that by linguistic convention are ancillary and as such discursively secondary in relation to other linguistic expressions, and that grammaticalization is the kind of change that gives rise to such expressions