1. What Are Modals of Probability?

Modals of probability are used to express how certain or uncertain you are about something. Instead of stating a fact, you express your deduction, possibility or conclusion based on evidence.

2. The Certainty Scale

Each modal expresses a different level of certainty — from near certain to almost impossible.

3. MUST — Near Certain Positive Deduction

Use must when you are almost certain something is true based on evidence. It is a logical conclusion.

Konan has been studying for 12 hours. He must be exhausted. (Konan étudie depuis 12 heures. Il doit être épuisé.)
She passed the BAC with 18/20. She must have studied very hard. (Elle a eu 18/20 au BAC. Elle a dû beaucoup travailler.)
Look at that crowd! The concert must be amazing. (Regarde cette foule ! Le concert doit être incroyable.)

4. CAN'T / COULDN'T — Near Certain Negative Deduction

Use can't or couldn't when you are almost certain something is NOT true — the opposite of must.

He just ate a huge meal. He can't be hungry again already! (Il vient de manger énormément. Il ne peut pas avoir faim déjà !)
She left only five minutes ago. She can't have arrived yet. (Elle est partie il y a seulement cinq minutes. Elle ne peut pas encore être arrivée.)
That can't be Aminata — she is in Bouaké this week. (Ce ne peut pas être Aminata — elle est à Bouaké cette semaine.)

5. MIGHT / MAY / COULD — Expressing Possibility

Use might, may, or could when something is possible but uncertain. They express different degrees of possibility.

She isn't here yet. She may be stuck in traffic. (Elle n'est pas encore là. Elle est peut-être bloquée dans les embouteillages.)
I'm not sure about the meeting time. It might start at 9 or at 10. (Je ne suis pas sûr de l'heure de la réunion.)
He didn't answer. He could have been sleeping when you called. (Il dormait peut-être quand tu as appelé.)
She might have forgotten about the meeting — let's remind her. (Elle a peut-être oublié la réunion.)

6. SHOULD — Expressing Expectation

Use should when you expect something to be true based on what is normal, planned or logical.

I sent the package three days ago. It should arrive today. (Il devrait arriver aujourd'hui.)
He studied all week. He should pass the exam easily. (Il devrait facilement réussir l'examen.)
The results should have been published yesterday — I wonder what happened. (Les résultats auraient dû être publiés hier.)

7. Present vs Past Deductions — Full Comparison

8. Real-Life Contexts — Examples from Côte d'Ivoire

✅ MUST (almost certain) :
Adjoua hasn't eaten since this morning. She must be very hungry by now.
Kouamé got 19/20. He must have prepared really well for the BEPC.

MIGHT/MAY (possible) : The teacher isn't here yet. She might be stuck in traffic on the boulevard.

CAN'T (impossible) : That can't be Konan's score — he never fails English!

COULD HAVE (past possibility) : He didn't show up. He could have forgotten about the appointment.

9. Common Mistakes to Avoid

✘ He mustn't be wrong. ✔ He can't be wrong. (negative deduction = can't, not mustn't)
→ MUSTN'T = prohibition ("you must not"). CAN'T = near certain it's not true.

✘ She might have forgot the keys. ✔ She might have forgotten the keys. (modal + have + past participle)
→ After modal + have, always use the past participle, not the base verb.

✘ He could be have left already. ✔ He could have left already. (modal + have + past participle — no "be")
→ Past deduction structure : modal + HAVE + past participle. Never insert "be" between have and the participle.