Modal Verbs — English Bac Sciences Humaines

Dans le programme du Bac Sciences Humaines

English carries a coefficient of 3 in the Bac Sciences Humaines stream — level with Arabic Language, just behind History-Geography, Philosophy and French (coefficient 4). It is a genuine average-mover, and the humanities focus of the stream makes its themes on society, citizenship, culture and development especially familiar territory.

À l'épreuve

Three parts: Reading Comprehension, Language, and Writing (a guided text of about 180 words, longer at the top of the mark range). Sciences Humaines candidates, used to handling ideas and social questions, can bring real substance to essay prompts on culture, citizenship and development — the discipline needed is to keep the writing in clear, accurate English.

Objectifs d'apprentissage

Apply this grammar point accurately in the Language section and in the guided writing of the Bac Sciences Humaines English exam (coefficient 3)
Distinguish can / could (ability, informal permission) from may / might (possibility, formal permission)
Distinguish must (obligation imposed by the speaker) from have to (obligation imposed by an outside rule)
Contrast must not (prohibition) with don't have to (absence of obligation)
Use must, can't and may / might / could to express a logical deduction

Notions clés

Ability, permission and possibility

can (present ability, informal permission), could (past ability, polite request), may / might (possibility, formal permission — might expresses a weaker possibility than may).

Obligation and advice

must (obligation the speaker imposes), have to (obligation an outside rule imposes); must not (prohibition) and don't have to (absence of obligation, the action is still allowed) are opposite meanings; should / ought to (advice, recommendation).

Logical deduction

must expresses a near-certain positive deduction (“He must be tired”), can't a certain negative deduction (“She can't be at home, the lights are off”), may / might / could an uncertain deduction, a mere possibility.

Erreurs fréquentes

Confusing must not (prohibition) with don't have to (absence of obligation, the action is still allowed) — opposite meanings.

Adding to after a modal: “must to go” is wrong — must is always followed by the base form without to (have to is the exception, since have is the finite verb).

Using must for a deduction about the past without have: a past deduction is must have + past participle, not must + past participle.

Exemple corrigé

Énoncé

Choose the right modal and justify: “The lights are off and the car isn't in the driveway. They ___ be at home.” (must / can't / should)

Correction

Weigh the evidence. Lights off and car gone are strong evidence that they are NOT at home.

Choose the right deduction. A certain negative deduction is marked by can't, not must (which would mean the opposite).

Result. “They can't be at home.” (must would mean “they must be at home”, which contradicts the evidence).

Le cours, puis l'entraînement.

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3 exercices pour t'entraîner

Exercice 1

Easy

Complete with must or mustn't: “You ___ smoke in the hospital, it's strictly forbidden.”

Voir la correction

mustn't — a formal prohibition, not an absence of obligation.

Exercice 2

Medium

Complete with have to or don't have to: “It's Saturday, so I ___ go to work today.”

Voir la correction

don't have to — absence of obligation (it is Saturday, going to work is not required), not a prohibition.

Exercice 3

Hard

Correct: “She must has finished the report by now.”

Voir la correction

A deduction about a completed fact is formed with must have + past participle: “She must have finished the report by now.”

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Questions fréquentes

must and have to — what is the real difference in the exam?

In meaning both express obligation, but must comes from the speaker (“I must call my mother”) and have to comes from an outside rule or authority (“I have to wear a uniform at school”). The Bac often accepts both in the affirmative but mostly tests their opposite forms in the negative.

How do I recognise a logical-deduction exercise?

The context gives clues (“the lights are off”, “she got an A”) from which you must conclude: must for a near-certain positive conclusion, can't for a certain negative conclusion, might / may / could for a mere possibility.

Can must be used in the past?

must itself has no past form for obligation (use had to); but for a deduction about a past fact, keep must and add have + past participle: must have finished, must have left.

How much English revision does a coefficient-3 subject deserve in my stream?

A regular slot, not an afterthought. Fix each chapter's rule or vocabulary with two examples, write a short essay every week, and use the society themes — where your stream gives you ideas — as your strongest material. Keep a reusable introduction and conclusion, and check accuracy as you go.

Is this grammar point actually tested on the Bac Sciences Humaines English paper?

Yes — in the Language section as gap-fill, sentence-joining or error-correction, and indirectly in Writing, where the same structures decide whether a sentence is marked as accurate. One rule, two examples and one typical mistake per point is enough to cover both.