This study enamines the perception of stressed and unstressed versions of the modal auxiliary can for the listening comprehension of non-native speakers of English. The results show that the non-native subjects of this study did distinguish differences in meaning between stressed and unstressed recordings of the auxiliary in sentences, choosing to assign a negative form can't signtficantly more often when presented with a stressed form of can compared with an unstressed (reduced) form of the same word. The importance of prosody in English teaching is discussed in relation to the results of the study.