How do present modals of deduction with must, might, and can't work?
Must marks a sure positive conclusion, can't a sure negative conclusion, may/might/could a possibility, and should an expectation. Follow them with be or be plus an -ing form.
- Must be = sure positive conclusion; can't be = sure negative conclusion.
- May, might, and could keep the deduction possible.
- Should expresses an expectation about the present.
B1 · Modals · 10 minPresent deduction: choose must, might, and can't with confidence.
This B1 lesson gives you a certainty ladder for deductions about the present. Distinguish sure positive and negative conclusions, possibilities, and expectations in everyday and office situations — free to try, with no signup.
- CEFR levelB1 · Intermediate
- Time to completeAbout 10 minutes
- Core choiceCertainty of the deduction
- Blocks10 blocks
01 / 07
How do you use present modals of deduction with must, might, and can't?
Use present modals of deduction by choosing the modal that matches your certainty: must for a sure positive conclusion, can't for a sure negative conclusion, and may, might, or could for a possibility. If a blocked calendar leads you to conclude that a colleague is in a meeting now, say "She must be in a meeting." If an empty parking space shows that a colleague cannot be at the office, use "He can't be in the office — his car isn't there." When you are not certain, "She might be with a client" keeps the situation possible. In this use, the modals show the strength of your present conclusion. Start by asking how certain the deduction is, then choose its rung on the ladder.
02 / 07
What is the difference between must be and can't be?
The difference between must and can't is the direction of the sure conclusion: must confirms a positive deduction, while can't confidently rules something out. In "She must be in a meeting," you conclude that her presence there is certain. In "He can't be in the office," you conclude that his presence at the office is impossible. Both forms therefore express strong certainty, but they point in opposite directions. This contrast matters because a negative deduction does not use must plus not. Instead, English selects can't. Keep the minimal pair "It must be right" and "It can't be right" together. The first sentence confirms the conclusion; the second excludes it. Choosing positive or negative direction before the form prevents the central error.
03 / 07
When do you use may, might, or could for present speculation?
Use may, might, or could when a present explanation is possible but you do not want to present it as certain. In this lesson, all three belong to the possibility rung. If a colleague is away from her desk, "She may be with a client," "She might be with a client," or "She could be with a client" can offer an open explanation. None of those statements claims that the explanation is settled. That separates them from sure positive must and sure negative can't. At B1, you do not need to build a fine ranking among these three choices here; first recognise their shared function. When the context supplies only perhaps or one open explanation, choose a possibility modal. When it marks the conclusion as sure, move to must or can't.
04 / 07
When does should express a present expectation?
Use should for an expectation when a result is expected from the current plan or course of events without being presented as a sure conclusion. "The report should be ready by Friday" says that the report is expected by Friday. It does not use must to claim certainty, and it does not leave the result as merely one unstructured possibility. In office contexts, this form fits plans, figures, or documents whose expected status matters: "The figures should be ready." Compare the jobs of the forms: must gives a sure positive conclusion, may/might/could give a possibility, and should gives an expectation. Do not ask only whether the statement sounds positive. Decide whether you mean a conclusion, an open possibility, or an expected result.
05 / 07
How do you form modals of speculation in the present?
Form present deductions with a modal plus be, or with a modal plus be and an -ing form. For a state or identity, use sentences such as "She must be in a meeting" or "This email can't be from Anna." For an action in progress now, use "The client must be looking at last quarter's figures." The modal does not change, and no to appears directly after it. In speech, also notice weak must before a consonant. In "must be," it can sound like /məs(t) biː/; strong /mʌst/ appears when stressed. Deductions about the past use a different structure with must have plus a participle. That past form belongs to the follow-on B2 lesson and remains only a pointer here.
06 / 07
Why is mustn't wrong for a negative deduction?
Mustn't is wrong for a negative deduction because it expresses prohibition; a sure negative conclusion needs can't. The intended meaning in "He can't be in the office" is that his presence is impossible. "He mustn't be in the office" instead says that being there is prohibited. The same contrast corrects "This email mustn't be from Anna" to "This email can't be from Anna." German learners also need to separate German sollen used for hearsay from English should used for expectation. "The boss should be ill" does not carry that hearsay meaning. Use "The boss is said to be ill" or "Apparently, the boss is ill." Keep negative deduction, prohibition, expectation, and hearsay as four separate communicative jobs.
07 / 07
How do you use present deduction modals at work?
At work, use deduction modals to classify a current situation according to the available degree of certainty. With an obviously impossible total, say "The invoice can't be right." When a colleague's calendar is blocked, "She must be in a meeting" gives a sure positive conclusion. Without firm clues, leave a possibility open: "She might be with a client." For an agreed schedule, state an expectation: "The figures should be ready by Friday." You can also classify an action in progress, as in "The client must be looking at last quarter's figures." These choices show whether you rule something out, conclude it strongly, keep it possible, or expect it. Read the situation first, name your certainty, then add the modal plus be or be plus an -ing form.