ABSTRACT:  This paper provides a comprehensive description of the semantics of can, may, could and might in three parallel corpora of contemporary British, American and Australian English. Even though the modals investigated can express the same meanings, paradoxically there is little semantic overlap between them in the data. For example, the meanings of can and may appear to merge in a sentence such as It can/may be cold in Stockholm, but a distinction is discernible between the theoretical dynamic sense of can and the general present epistemic sense of may. The domain of dynamic possibility is dominated by can and could, that of epistemic possibility by may and might. In the latter case the traditional supremacy of may is being threatened by might, especially in American and Australian usage; could is emerging as an exponent of the same meaning; and instances of can that are not restricted to non-affirmative contexts are beginning to appear.