Section 11.4 Semi-Modals (Quasi-Modals)
The nine modal auxiliaries have a strict set of grammatical properties: no -s ending, no infinitive with to, no -ing or past participle forms. But English also has a set of expressions that carry similar meanings through different grammatical machinery. Have to means roughly the same thing as must, but unlike must it inflects: She has to leave. Be going to expresses future intention like will, but it uses the progressive construction. These expressions—called semi-modals or quasi-modals—fill gaps that the true modals leave. Because they behave more like ordinary verbs, they can appear in tenses and forms that true modals cannot.
Common Semi-Modals.
| Semi-modal | Meaning | Example |
|---|---|---|
| have to | necessity | I have to leave. |
| have got to | necessity (informal) | I’ve got to go. |
| be able to | ability | She’s able to help. |
| be going to | future intention | I’m going to study. |
| be supposed to | expectation/obligation | You’re supposed to wait. |
| be allowed to | permission | We’re allowed to leave. |
| ought to | obligation | You ought to apologize. |
| used to | past habit | I used to live there. |
Semi-modals vs. True Modals.
Unlike true modals, semi-modals:
-
Can be inflected: She has to go. (third person -s)
-
Can follow other modals: You will have to leave.
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Can take -ing or infinitive forms: Having to leave upset her.
This flexibility is precisely what makes semi-modals useful. Because true modals cannot be inflected or combined, English needs semi-modals to express modal meanings in certain grammatical contexts. You cannot say I can must leave, but you can say I might have to leave—the semi-modal have to fills the gap.
