This article sheds new light on the usage constraints of be able to, by combining empirical evidence from the British National Corpus (BNC, Davies 2004–) with theoretical insights on the semantics–pragmatics interface. First, we show that be able to does not, contrary to the general assumption, express only ‘ability’ but it shares most of the root meanings usually associated with the possibility modals can and could (Coates 1983: 124). The data analysis shows that what is called ‘opportunity’ in Depraetere & Reed's (2011) taxonomy is the most frequent meaning of be able to. We then turn to the notion of actualisation, which is often claimed to be the main distinguishing feature between be able to and can/could. The qualitative analysis of the BNC dataset provides the empirical evidence, lacking in previous research, for the claim that actualisation is indeed a defining property of the modal periphrastic form. Starting from a reassessment of the semantics–pragmatics interface in terms of a fourfold distinction, we argue that actualisation is a generalised conversational implicature and constitutes conventional pragmatic meaning (that is, conventional non-truth-conditional meaning).