Intuition: one plausible possibility
Use might be and could be when the speaker has seen or knows something but lacks enough information for a certain conclusion. They do not assign a mathematical certainty percentage; they honestly signal that an explanation is possible and alternatives exist.
A good guess draws on the available context. If a colleague is not answering during a work meeting, She might be in a meeting is an appropriate suggestion. Do not automatically strengthen it to must be without evidence.
subject + might/could + be + possible state, identity or location
- subject / S —
- The grammatical subject: who or what the clause is about; the verb agrees with it. In The book was written, the book is the subject, although someone else does the action.
She's not answering; she might be in a meeting.
She's not answering; she might be in a meeting.
There is no certainty: a meeting is only one plausible explanation.
The noise could be the heating.
The noise could be the heating.
Could be presents the noise’s source as a possibility rather than an established fact.
Form: no to and no -s
Might and could are modal verbs. Use base-form be after them, not is, to be or a form with -s. The modal does not change by person: I might be, she might be, they could be.
In a question, the modal can precede the subject, but this rule mainly targets statements offering guesses. Could you be quieter? has the correct form but another function: it is a request.
I/you/he/she/it/we/they + might/could + be
It could be a delivery for the office.
It could be a delivery for the office.
Could is followed by unchanging base-form be.
Mina might be busy now.
Mina might be busy now.
A third-person subject adds no -s to might or be.
What can follow be?
After be, use an adjective for a state, a noun phrase for a role or identity, or a prepositional phrase for a location. To suggest an action happening now, use might/could + be + an -ing verb.
There could be + noun expresses the possible existence of something: There could be traffic. There belongs to the existential construction, and be still keeps its base form after the modal.
might/could be + adjective / noun / location / V-ing; there might/could be + noun
- verb / V —
- A word for an action or state, such as work or be. The pattern determines its form.
- V-ing / -ing —
- The verb form ending in -ing: working, going. Its role depends on the construction.
- noun —
- A word naming a person, thing or idea: student, book, happiness.
- adjective —
- A word describing what someone or something is like: happy, tired, interesting.
Ravi might be tired.
Ravi might be tired.
The adjective tired names a possible state.
The woman at the desk could be the manager.
The woman at the desk could be the manager.
The noun phrase the manager names a possible role.
They might be waiting outside.
They might be waiting outside.
Be waiting expresses a possible ongoing action.
There could be delays this evening.
There could be delays this evening.
There could be introduces the possible existence of delays.
Might, could and may
In guesses about the present or future, might, could and may often express the same basic idea: something is possible, but the speaker is uncertain. Might be and could be are therefore natural alternatives in many neutral contexts.
The three modals are not mechanically interchangeable in every situation. May is more common in formal announcements, while choice, stress and wider context can affect the nuance. Might be/could be are the active target here; grammatical may be is not an error merely because its register differs.
The train might be late.
The train might be late.
A neutral guess without a claim of certainty.
The train could be late.
The train could be late.
In this context, could be expresses the same plausible possibility.
Some services may be unavailable.
Some services may be unavailable.
May is natural in a formal announcement; the contrast is stylistic, not a grammatical error.
Negative possibility
Might not be presents a negative state as possible: The room might not be ready. It differs from can’t be, which in deductions expresses a strong conclusion of impossibility.
Could not and couldn’t have several functions, including inability and strong rejection of a possibility. To express a clear uncertain negative guess at B1, we practise might not be rather than automatically replacing it with couldn’t be.
subject + might not + be + state, identity or location
- subject / S —
- The grammatical subject: who or what the clause is about; the verb agrees with it. In The book was written, the book is the subject, although someone else does the action.
The room might not be ready yet.
The room might not be ready yet.
The speaker allows for the negative possibility without asserting it.
Leah might not be at her desk.
Leah might not be at her desk.
Might not be leaves both possibilities open.
Not every could or might is a guess
Could also expresses past ability, requests, suggestions or conditional possibility. Might can express formal permission or reported may. The whole sentence and situation determine the function, rather than a single word.
For a guess, look for a possible answer to “what is true now or could be true later?” Could you be quiet? requests an action; When I was five, I could swim describes ability; She said he might be busy reports someone’s words. All are grammatical, but not all target this rule’s deduction function.
The caller could be our new supplier.
The caller could be our new supplier.
A guess about the caller’s identity.
Could you be quieter, please?
Could you be quieter, please?
A polite request rather than a factual guess.
When I was six, I could swim.
When I was six, I could swim.
Could describes past ability here, rather than present possibility.
Using the forms in speech
A natural guess often has two parts: brief evidence and a cautious conclusion. First state what is known, then add one or more plausible possibilities with might be/could be.
Do not invent exact percentages or artificial distinctions between might and could. Preserve the facts, avoid overstating the evidence and show that the conclusion remains open to checking.
Her bag is here, but she isn't. She might be in the kitchen.
Her bag is here, but she isn't. She might be in the kitchen.
The first sentence gives evidence; the second offers a cautious explanation.
The screen is frozen. It could be a network problem, or the app might be updating.
The screen is frozen. It could be a network problem, or the app might be updating.
Two different modals present two open alternatives.
Common mistakes
Incorrect:She might is in a meeting.
Correct:She might be in a meeting.
Modal might requires base-form be, not is.
Incorrect:There could to be a delay.
Correct:There could be a delay.
After could, use an infinitive without to.
Incorrect:He mights be at reception.
Correct:He might be at reception.
Modals take no third-person -s.
Incorrect:They don't might be ready.
Correct:They might not be ready.
Negate might without auxiliary do: might not.
Incorrect:The parcel could be arrives today.
Correct:The parcel could arrive today.
Could requires a base verb. If that verb is be, give it an appropriate complement, such as could be late, rather than finite arrives.