English Modal Verbs of Possibility

Modal verbs of possibility in English are used to express how certain or uncertain we are about a present or future situation. The primary modal verbs used for this purpose are 'must', 'might', 'could', 'may', and 'can't'. Each verb conveys a different level of logical deduction or probability.

We use 'must' when we are almost 100% sure that something is true based on strong evidence (e.g., 'He must be tired after working all night'). On the other end of the scale, we use 'can't' when we are almost 100% sure that something is impossible (e.g., 'She can't be at home, I saw her leave'). For intermediate uncertainty, 'might', 'may', or 'could' are used to indicate that something is possible but not certain (e.g., 'It might rain later').

It is a common grammatical error to use 'mustn't' to express negative certainty; 'mustn't' means prohibition, whereas 'can't' must be used for logical impossibility. Understanding these nuances allows English learners to make assumptions, state deductions, and qualify their assertions accurately in daily communication.