The modal auxiliary can occasionally occurs, as it seems redundantly, in sentences like “I can promise that you'll like it”, a usage that has sometimes been difficult to explain. Its occurrence in the CobuildDirect Corpus is here investigated, and it appears that it typically occurs with three types of verbs: performative verbs, verbs of perception and verbs of mental processes. Far from being redundant, it carries out a number of important functions, labelled Shock absorber, Empathiser/Emphasiser and Qualifier. It is finally suggested that its use in those functions will explain why it predominantly occurs with the three types of verbs.