Modality: Syntactic reference¶
Must¶
Minimal contrasts¶
He must leave. (obligation; plain infinitival clause)
He must be leaving. (present ongoing inference; progressive infinitival clause)
He must have left. (past inference; perfect infinitival clause)
He had to leave. (past obligation; finite clause; not a modal construction)
Licensed constructions¶
He must leave. (obligation; plain infinitival clause)
He must leave tomorrow. (future obligation; plain infinitival clause)
He must be at home. (present inference; plain infinitival clause)
He must know the answer. (present inference; plain infinitival clause)
He must be sleeping. (present ongoing inference; progressive infinitival clause)
He must be working. (present ongoing inference; progressive infinitival clause)
He must be arrested. (obligation; passive infinitival clause)
He must have left. (past inference; perfect infinitival clause)
He must have seen us. (past inference; perfect infinitival clause)
He must have been sleeping. (past ongoing inference; perfect progressive infinitival clause)
He must have been working all day. (past ongoing inference; perfect progressive infinitival clause)
He must have been arrested. (past inference; perfect passive infinitival clause)
The report must have been completed already. (past inference; perfect passive infinitival clause)
You mustn’t leave. (prohibition; plain infinitival clause)
You mustn’t tell anyone. (prohibition; plain infinitival clause)
Ungrammatical¶
He must to leave.(plain infinitive required)
He must left.(plain form required)
He must have saw it.(past participle required)
He must had left.(perfect infinitive required)
He must have had seen us.(past participle required)
He must leaving.(plain form required)
To must leave is difficult.(no non-finite forms)
Technical notes¶
No preterite form.
No non-finite forms.
No to-infinitive complement.
Past obligation normally uses had to, not must.
Mustn’t expresses prohibition, not lack of necessity.
Negative epistemic must not is possible but rare; it expresses a strong negative inference:
He must not know the answer. (negative inference)
Can¶
Minimal contrasts¶
He can swim. (ability; plain infinitival clause)
He can be swimming. (present ongoing possibility; progressive infinitival clause)
He can have swum. (past possibility; perfect infinitival clause)
He could swim. (past/general ability; preterite modal)
He was able to swim. (specific successful past ability)
Licensed constructions¶
He can swim. (ability; plain infinitival clause)
He can solve the problem. (ability; plain infinitival clause)
He can leave now. (permission; plain infinitival clause)
He can be at home. (present possibility; plain infinitival clause)
He can be sleeping. (present ongoing possibility; progressive infinitival clause)
He can be seen from the road. (possibility; passive infinitival clause)
He can have left already. (past possibility; perfect infinitival clause)
He can have forgotten. (past possibility; perfect infinitival clause)
He can have been sleeping. (past ongoing possibility; perfect progressive infinitival clause)
He can have been arrested. (past possibility; perfect passive infinitival clause)
You can’t enter. (prohibition; plain infinitival clause)
You can’t be serious. (present impossibility; plain infinitival clause)
He can’t have done it. (past impossibility; perfect infinitival clause)
The door can’t have been locked. (past impossibility; perfect passive infinitival clause)
Ungrammatical¶
He can to swim. (plain form required)
He can swims. (plain form required)
He can swimming. (plain form required)
He can swam. (plain form required)
He has can swim. (no participle form)
He is can swim. (no non-finite form)
To can swim is useful. (no infinitive form)
Technical notes¶
No infinitive form (to can is not possible).
No participial forms as a modal (canning, canned are not modal forms).
No third-person singular -s (he cans is not modal can).
Past ability may require was/were able to for a specific successful event:
She was able to escape.
Negative can’t has two distinct uses:
He can’t swim. (inability)
He can’t have left already. (impossibility)
Could¶
Minimal contrasts¶
He could swim. (past general ability; plain infinitival clause)
He could be swimming. (present ongoing possibility; progressive infinitival clause)
He could have swum. (past possibility; perfect infinitival clause)
He was able to swim. (specific successful past ability)
Licensed constructions¶
He could swim. (past general ability; plain infinitival clause)
He could solve the problem. (past general ability; plain infinitival clause)
He could leave early. (permission; plain infinitival clause)
He could be at home. (present possibility; plain infinitival clause)
He could be sleeping. (present ongoing possibility; progressive infinitival clause)
He could be seen from here. (possibility; passive infinitival clause)
He could have left already. (past possibility; perfect infinitival clause)
He could have forgotten. (past possibility; perfect infinitival clause)
He could have been sleeping. (past ongoing possibility; perfect progressive infinitival clause)
He could have been arrested. (past possibility; perfect passive infinitival clause)
You couldn’t enter. (lack of ability/permission; plain infinitival clause)
He couldn’t be serious. (present impossibility; plain infinitival clause)
He couldn’t have done it. (past impossibility; perfect infinitival clause)
The door couldn’t have been locked. (past impossibility; perfect passive infinitival clause)
Ungrammatical¶
He could to swim.(plain form required
He could swims.(plain form required)
He could swimming.(plain form required)
He could swam.(plain form required)
He has could swim.(no participle form)
He is could swim.(no non-finite form)
To could swim is useful.(no infinitive form)
Technical notes¶
Preterite form of can.
No infinitive form (to could is not possible).
No participial forms as a modal (coulding, coulded are not modal forms).
No third-person singular -s (he coulds is not possible).
Expresses past general ability, not normally a specific successful past event.
Frequently marks modal remoteness (tentativeness, politeness, hypotheticality) rather than past time.
Could have + past participle expresses past possibility, not past ability. For a specific successful event, was/were able to is normally preferred.
MAY¶
Licensed constructions¶
He may leave now. (permission; plain infinitival clause)
He may take another copy. (permission; plain infinitival clause)
He may be at home. (present possibility; plain infinitival clause)
He may know the answer. (present possibility; plain infinitival clause)
He may be sleeping. (present ongoing possibility; progressive infinitival clause)
He may be seen from the road. (possibility; passive infinitival clause)
He may have left already. (past possibility; perfect infinitival clause)
He may have forgotten. (past possibility; perfect infinitival clause)
He may have been sleeping. (past ongoing possibility; perfect progressive infinitival clause)
He may have been arrested. (past possibility; perfect passive infinitival clause)
You may not leave yet. (permission withheld; plain infinitival clause)
He may not be at home. (present possibility (negative); plain infinitival clause)
He may not have seen us. (past possibility (negative); perfect infinitival clause)
Minimal contrasts
He may leave now. (permission; plain infinitival clause)
He may be sleeping. (present ongoing possibility; progressive infinitival clause)
He may have left. (past possibility; perfect infinitival clause)
He may have been sleeping. (past ongoing possibility; perfect progressive infinitival clause)
Ungrammatical
He may to leave. (plain form required)
He may leaves. (plain form required)
He may leaving. (plain form required)
He may left. (plain form required)
He has may leave. (no participle form)
He is may leave. (no non-finite form)
To may leave is permitted. (no infinitive form)
Technical notes No preterite form. No infinitive form (to may is not possible). No participial forms as a modal (maying, mayed are not modal forms). No third-person singular -s (he mays is not possible). Used for both permission and epistemic possibility. May not is ambiguous:
permission withheld:
You may not leave yet.
negative possibility:
He may not be at home.