'Could' vs. 'Be Able To': How to Use Modals in English Grammar In this episode, we investigate the differences in meaning, from and use between the modals  'can',  'could' and 'be able to.' We pay particular attention to the strange anomaly of learners inaccurate grammar usage of 'could' to express a single positive action in the past. English Weirdness is a video series that explores and investigates the strange side of the English language, its irregular grammar, contradictory syntax rules, and even the oddities created by learners as they attempt to navigate the complexities of this language made up of Latin, French, Celt, and German influences. The series is the creation of English-as-Second Language instructor Paul Duke from Vancouver, BC.