We use modals of possibility or probability to make a guess or draw a logical conclusion about an activity in progress at the present time; that is, during the time of speaking.
Formula: SUBJECT + APPROPRIATE MODAL + BE + ING VERB
Person A: What’s all that noise?
Person B: The neighbour’s son is in a rock band. They must be practicing.
We also use modals of possibility or probability to make guesses or logical conclusions about past activities.
Formula: SUBJECT + APPROPRIATE MODAL + HAVE BEEN + ING VERB
Person A: I didn’t hear a sound when I passed by the children’s room earlier.
Person B: They must have been sleeping.
Must, could, might, may, couldn’t, can’t, may not and might not are used to show how certain the speaker is that an action is presently occurring or not occurring. Using must conveys a strong feeling of certainty; nevertheless, there is still some doubt in the speaker’s mind.
Could, may and might show that a speaker is 50% or less certain that an action is in progress.
Couldn’t and can’t show that the speaker believes strongly that a situation is not taking place. For example:
It’s noon. George went to bed at 10:00 last night. He can’t still be sleeping!
May not and might not convey the idea that a speaker is 50% or less certain that an action is not possible or probable. They are not normally used in their contracted forms.
Correct: They aren’t here yet and it’s getting late. They might not be coming.
Incorrect: They aren’t here yet, and it’s getting late. They mightn’t be coming.
Might and could are used in questions regarding the possibility or probability of actions taking place. However, may and must are not.
Correct: Could Tom be studying now?
Incorrect: May Tom be studying now?
For most short answers, a modal alone is used. However, if the question includes a be verb, a modal with be is required.
Person A: Is Simon joining us?
Person B: I’m not sure. He might be.
Remember that not all verbs are used in the continuous (progressive) form. Non-action verbs that describe situations or conditions that aren’t expected to change, such as seem, appear, cost, weigh, have and be are not used. Other types of non-continuous verbs are:
- Verbs of the senses (hear, smell, see, taste, etc.)
- Verbs of ownership (have, belong, own, possess)
- Verbs that convey feelings (love, hate, like, hate, prefer, want, etc.)