Expressing Probability in English

Expressing Probability in English: May, Might, Will, Must & More

Hello English learners! Welcome to a new lesson. Today, we’re going to discuss expressing probability in English — in other words, how we say how likely or unlikely something is to happen or to be true. This topic is extremely important for everyday conversation, writing (especially opinions, essays, and reports), and Cambridge exams (B2 First, C1 Advanced)

English uses modal verbs, adverbs, and adjectives to show different degrees of certainty.

A probability scale (from 0% to 100%)

Think of probability like a scale:

• 100% certain: will, must, definitely, certainly
• 70–90% likely: probably, likely
• 40–60% possible: may, might, could, possibly
• 0–10% unlikely: probably won’t, unlikely, impossible, can’t

This scale will help you choose the right word for how sure you are.

Modal verbs for probability

May / Might / Could (Possibility)

We use may, might, could when something is possible, but not certain.

• They may come to the party.
• It might rain later.
• She could be at home.

Might is often a little less certain than may, but the difference is small.

Will (strong certainty / confident prediction)

We use will when we are very sure about something.

• She will be here at 7.
• That film will win awards.

Must / can’t (logical deduction)

We use must when something is almost certainly true based on evidence.

We use can’t when something is almost certainly impossible.

• The lights are on. They must be at home.
• He’s only 12. He can’t be the manager.

Adverbs of probability

Adverbs help us show how sure we are.

Word order with adverbs

Adverbs of probability usually go after the modal verb or before the main verb.

✅ She will probably arrive late.

✅ They might possibly cancel the match.

❌ Probably she will arrive late. (awkward)

Adjectives of likelihood

We often use:

It is + adjective + that + clause

• It is likely that she’ll get the job.
• It is unlikely that we’ll finish today.

Very common mistakes – Expressing Probability in English

❌ He must to be tired.

✅ He must be tired.

❌ She will probably to come.

✅ She will probably come.

❌ It is likely she will win.

✅ It is likely that she will win.

How to choose the right form

Ask yourself – how sure am I?

Almost 100%? → must / will / definitely

Quite sure? → probably / likely

Not sure? → may / might / could / possibly

Almost impossible? → can’t / unlikely / impossible

Final thought

Good English isn’t just about saying what you think — it’s about showing how sure you are. Mastering probability words will make your English more precise, more natural, more persuasive and much more exam-ready.

After all, in English (and in life), very few things are 100% certain… except grammar mistakes in a first draft. 😄

Do the quiz to perfect your knowledge:

 FAQ 

What modal verbs express probability in English?

May, might, could, must, will and can’t are commonly used to express different levels of certainty.

What is the difference between must and can’t for probability?

Must is used for strong logical deduction (almost certain). Can’t is used when something is almost certainly impossible.

Is “may” more certain than “might”?

May and might both express possibility. Might is sometimes slightly less certain, but the difference is small in modern English.

Where do adverbs of probability go in a sentence?

They usually go after modal verbs (She will probably come) or before the main verb (She probably knows).

Related posts:

Modal verb MUST

Modal verbs MAY & MIGHT

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