Blog about English
Expressing possibility, probability, deduction and certainty using modal verbs.
Modal verbs and related expressions can show how possible, probable, or certain the speaker believes a situation to be.
Common forms include may, might, could, can, must, should, will, be likely to, and be certain to.
May expresses a possibility that the speaker considers realistic or plausible.
For example, It may rain this afternoon and She may be at home.
Might expresses possibility and is often more tentative than may.
For example, We might go out tonight and He might be working late.
Could can express a possible situation or possible future event.
For example, It could rain later and She could be at the office.
Can can express general or theoretical possibility rather than a prediction about one particular event.
For example, Accidents can happen and Winters can be very cold here.
May, might, and could can all express possibility, with differences often involving tentativeness, context, or speaker perspective rather than a fixed probability scale.
For example, It may rain, It might rain, and It could rain can all describe a possible future event.
Must can express a strong logical conclusion based on available evidence.
For example, The lights are on, so they must be home.
Cannot or can't can express that a situation is logically impossible or extremely unlikely based on evidence.
For example, That cannot be true and She can't be serious.
Should can express an expectation that something is likely to happen or be true.
For example, The train should arrive soon and She should be home by now.
Will can express a confident prediction or expectation about a future event.
For example, She will probably arrive soon and That will be John at the door.
Be likely to expresses a high or moderate probability that something will happen or be true.
For example, Prices are likely to increase and He is likely to agree.
Be unlikely to expresses a low probability that something will happen or be true.
For example, They are unlikely to arrive before noon.
Be certain to expresses a very high degree of confidence that something will happen or be true.
For example, She is certain to succeed.
Probability can also be expressed with adverbs such as probably, certainly, definitely, perhaps, maybe, and possibly.
These adverbs often combine with modal verbs and other future expressions.
Probability adverbs have characteristic positions that can differ according to the verb structure.
For example, She will probably come, She has probably left, and She is probably at home.
Modal verbs can express uncertainty about a situation that is true or happening now.
For example, She may be tired, They might be waiting outside, and He could be at work.
Modal verbs can express uncertainty about future events.
For example, We may go tomorrow, It might snow tonight, and They could arrive late.
Modal perfect forms can express uncertainty or deduction about past events.
For example, She may have forgotten, They might have missed the train, and He could have taken the wrong road.
Must have + past participle expresses a strong conclusion about something that happened in the past.
For example, He must have forgotten the meeting and They must have left already.
Cannot have + past participle expresses that a past event is considered impossible or extremely unlikely.
For example, She cannot have forgotten; I reminded her yesterday.
May have and might have express possible past events or states.
For example, She may have missed the bus and They might have misunderstood the question.
Could have + past participle can describe a possible explanation for a past situation.
For example, He could have taken a different route.
Possibility and probability are related but not identical concepts.
A statement can be possible without being particularly probable. Context and the chosen modal or expression communicate the speaker's degree of confidence.
Different expressions can communicate different degrees of confidence, although their interpretation depends on context.
Expressions such as might, may, could, should, will, must, and be certain to can place a statement at different points on a continuum of confidence.
Modal deduction uses evidence to indicate how strongly the speaker believes a conclusion follows from the available facts.
For example, The ground is wet, so it must have rained and The ground is dry, so it cannot have rained recently.
Modal verbs can soften statements by presenting them as possibilities rather than facts.
For example, This may be the reason is less direct than This is the reason.
Formal writing frequently uses modal verbs and probability expressions to avoid presenting uncertain claims as absolute facts.
For example, The results may indicate, This could suggest, and The treatment is likely to improve outcomes.
Choose modal verbs and probability expressions according to the intended degree of possibility, probability, or certainty.
Common mistakes include confusing must for obligation with must for deduction, using can for a specific uncertain future event, confusing may not with must not, and using modal perfect forms incorrectly.