Verbs

Modal Auxiliaries

Modal auxiliary verbs — can, could, may, might, will, would, shall, should, must — team up with a main verb to express possibility, permission, necessity, or ability. In diagrams, the entire modal + verb phrase occupies the verb slot as a single unit.

Placement in Diagrams

A modal auxiliary verb and the verb it modulates form a single verb phrase. The whole phrase is placed on the right side of the baseline, just as any single verb would be.

“This must leak.”

Step 6 — demonstrative pronoun subject, modal + intransitive verb

This (demonstrative pronoun) is the subject. The complete verb is must leak — the modal must together with the present infinitive of the intransitive verb leak.

“Could rewards be offered?”

Step 7 — subjunctive modal + passive infinitive

rewards is the subject. The verb phrase Could be offered contains the subjunctive modal could and the basic present passive infinitive (without to).

“They should have hurried.”

Step 8 — modal + present perfect

“Homes may have been destroyed.”

Step 9 — modal + present perfect passive

“Who can help?”

Step 10 — interrogative pronoun subject, modal verb

Common Modal Auxiliaries

Modal	Core meaning	Example
can / could	ability; possibility	She can swim. He could help.
may / might	permission; possibility	You may leave. It might rain.
will / would	future; volition; conditional	We will go. I would prefer tea.
shall / should	obligation; expectation	You shall not pass. You should rest.
must	necessity; logical certainty	You must sign. This must be wrong.