The Mentalist Modal Verbs: Separate Possibility From Certainty
You know could, might, may, and must. Then real English starts moving fast and you accidentally turn a guess into a fact. The problem is not memorizing more modal verbs. It is matching your grammar to the evidence you actually have.
The most useful question is not “Which modal equals which percentage?” English does not work that neatly. Instead, ask two things: How strong is the claim? and what job is the modal doing here?
The Claim Ladder
- Information boundary: I do not know enough yet.
- Possibility: this is one plausible explanation.
- Probability: this seems more likely than not, but it is not settled.
- Strong inference: the circumstances strongly point this way.
- Claimed knowledge: the speaker presents the information as known.
These are not fixed percentages. Context, evidence, intonation, and surrounding language all matter.
Start with the boundary: say what you do not know
WE DON'T EVEN KNOW
This is excellent evidence-language because it prevents the conversation from racing ahead of the facts. Before choosing a confident modal, identify what is still unknown.
WHAT WE DO KNOW IS
Now the speaker separates confirmed information from speculation. This pair is more useful than a giant modal chart: first draw the boundary, then make the claim.
“We don't know why the train stopped. What we do know is that the delay has already passed forty minutes.”
Possibility: could and might keep the door open
THIS COULD BE
Could be presents one possible interpretation. It does not say the interpretation is likely, and it definitely does not make it a fact.
BECAUSE I THINK HE MIGHT KNOW
Here I think and might stack two layers of tentativeness. The speaker is giving an assessment, not claiming direct knowledge.
I THOUGHT IT MIGHT BE
This moves the uncertainty into the past: the speaker reports an earlier tentative belief.
- “The parcel could be at the neighbor's.”
- “Maya might be stuck in traffic.”
- “I thought the error might be in the spreadsheet.”
May and maybe are related in meaning—not in grammar
May is a modal verb. Maybe is an adverb. Learners often treat them as interchangeable pieces, but their sentence structure is different.
WELL, MAYBE.
Maybe can comment on an entire idea by itself. It is not a modal verb.
MAY I?
Here may is not about factual possibility at all. It asks permission.
Possibility: “She may have missed the email.”
Adverb: “Maybe she missed the email.”
Permission: “May I open the window?”
For a possible past event, may have + past participle and might have + past participle are common: “The courier may have left it downstairs.” That is a grammar pattern—not a claim that the event definitely happened.
Probability without a modal: chances are
MM-HMM. AND CHANCES ARE...
Chances are tells the listener the speaker sees an outcome as likely. It is a probability phrase, not a modal verb.
That matters because certainty in English is spread across modal verbs, adverbs, stance phrases, verbs such as think and know, and evidence language such as suggests.
Strong inference: must and has to are not the same as proof
HAS TO BE SLOCOMBE.
Here has to be expresses a strong conclusion from circumstances. It does not mean somebody is under an obligation to “be Slocombe.”
THIS RING MUST BE
Must be can also mark strong inference: the speaker feels the evidence makes another explanation difficult to accept.
Too strong: “He must be ignoring me.”
Better with weak evidence: “He might be busy. I don't know yet.”
Claimed knowledge sits on a different level
I KNOW WHAT HAPPENED.
Know presents the proposition as established from the speaker's perspective. That is categorically different from could, might, maybe, or chances are.
Of course, speakers can be wrong when they say “I know.” Grammar tells you how strongly they present the claim—not whether reality has certified it.
The same modal can do a completely different job
This is where certainty charts usually break down. A modal's meaning comes from the whole construction.
COULD I BOTHER YOU
Could is making a request more polite. It is not estimating whether bothering someone is possible.
OH, YOU MIGHT NOT WANT
Might softens advice here. The speaker is not assigning a probability to the listener's desire.
I COULD HAVE DONE THAT.
Could have + past participle describes a past option that was available but not taken in this context. Do not automatically interpret every could have as a guess about what happened.
| Form | Possible job | Writer-original example |
|---|---|---|
| could be | possibility | “It could be a caching issue.” |
| could you...? | polite request | “Could you resend the file?” |
| could have... | past option / sometimes past possibility | “We could have taken the earlier train.” |
| may | possibility or permission | “It may rain.” / “May I sit here?” |
| might | possibility or softened advice | “She might call.” / “You might want to save a copy.” |
| have to | necessity or, in has to be, strong inference | “I have to leave.” / “That has to be the entrance.” |
Evidence Before Grammar practice
Read the evidence first. Then choose wording that does not outrun it.
Missing parcel: tracking says “delivered,” but there is nothing at your door.
Model: “It could be with a neighbor.” / “The courier might have left it in the lobby.” You have plausible possibilities, not enough evidence for “The neighbor must have it.”
Late coworker: they normally arrive at 9:00; it is 9:08 and you have no message.
Model: “They might be running late.” Avoid “They must have missed the train” unless you have evidence about the train.
Weather: dark clouds are moving in and the forecast shows rain nearby.
Model: “It'll probably rain soon” or “Chances are it'll rain soon.” Stronger than a random possibility, still not direct knowledge.
Office error: the same wrong formula appears in every copied row, and the template contains that formula.
Model: “The template must be causing the error” can be a reasonable strong inference. Then verify it. Strong inference is still a step before confirmed diagnosis.
Travel delay: the airline has sent an official cancellation notice for your flight.
Model: “We know the flight is cancelled.” There is no reason to weaken confirmed information to “It might be cancelled.”
Friend not replying: you sent one message twenty minutes ago.
Model: “They might be busy.” Not “They must be upset with me.” Your evidence is tiny.
Three common certainty mistakes
1. Using must because you feel strongly
Must is about how the speaker frames an inference, not how emotionally convinced they feel.
2. Treating maybe and may as the same grammar
They can express similar uncertainty, but one is an adverb and the other is a modal verb.
3. Assuming cautious language is weak English
“I don't know yet,” “It could be,” and “The evidence suggests” are often more precise than an impressive-sounding certainty claim.
Practice the evidence, not just the modal
With FunFluen, pause before a character makes the next claim. Look at what is actually known in the scene, then predict whether the next line should sound possible, probable, strongly inferred, or known. Replay and compare the subtitle wording. Save useful certainty stems, then use Live AI Talk to practice upgrading and downgrading everyday claims so the grammar matches the evidence.
The rule worth keeping: choose certainty after you inspect the evidence—not before.
Explore more language-learning guides in FunFluen Learn.