Modals and related expressions
Modals are part of a verb phrase; they give more information about the main verb by qualifying it in some way. Modals also influence the grammar of the verb phrase; after a modal, the infinitive form (verb name) is used. Some modals can be used with different time references, present, past or future; others are restricted to one or two time frames. Some modals can be used in negative expressions, others cannot, and sometimes when used in a negative expression the usage changes. The chart below summarizes the time frames that are possible with the modals and their most common usages.
| Modal | Past | Present | Future | Usage |
|---|---|---|---|---|
| be able to | * | * | * | Shows ability I am / was / will be able / unable to do that. |
| be supposed to | * | * | * | Shows expectation I am / was supposed to / not supposed to do that.** |
| be to | * | * | * | Shows strong expectation I am / was to be / am not be there by noon / till noon.** |
| can / could | * | * | Shows ability or possibility—negative too I can / can't do that. I could / couldn't do that (tomorrow). | |
| * | Shows permission or lack of permission (informal, speaking only) You can / can't have that. | |||
| could | * | Request—formal Could you do that? | ||
| * | * | Shows suggestions You could do / have done that. Couldn't you do / have done that? | ||
| * | * | Shows limited certainty—under half They could be/ have been there. | ||
| * | * | Shows impossibility—negative The keys couldn't be / have been there. | ||
| had better | * | Shows advisability I had better / better not do that. | ||
| have got to | * | Shows necessity or lack of necessity I have got / haven't got to do that. | ||
| have to | * | * | * | Shows necessity or lack of necessity I have got/ had / will have to do that. I don't have/ didn't have / won't have to do that. |
| may | * | Formal request / permission May I have that? You may have that. | ||
| * | * | Shows limited certainty—under half I may/ may not do that later.** | ||
| might | * | Formal request Might I have that? | ||
| * | * | Shows limited certainty—under half I might do that/ I might not do that.** | ||
| must | * | * | Shows strong necessity I must take the car.** | |
| * | * | Shows prohibition You must not take the car.** | ||
| * | Shows very high certainty You must be tired after your journey. | |||
| ought to | * | * | Shows advisability I ought / ought not to do that.** | |
| * | * | Shows high certainty I ought to feel better tomorrow.** | ||
| shall | * | * | Formal question/suggestion Shall I do that?** | |
| should | * | * | Shows advisability I should / should not do that** | |
| * | * | Shows high certainty I should feel better tomorrow.** | ||
| used to | * | Repeated action in the past I used / used not to do that regularly. | ||
| will | * | * | Shows certainty / willingness I'll / wont be there I'll / won't do it. | |
| * | * | Formal request Will / won't you do that?** | ||
| would | * | * | Formal request Would you do that?** | |
| * | * | Shows preference I would rather/ would rather not do that.** | ||
| * | Repeated action in the past. I would do that years ago. | |||
| * | * | Shows advisability—negative I wouldn't do that (if I were you).** |
** present and future form is the same
Updated September 11, 2023 by Digital & Web Operations, University Relations (web_services@athabascau.ca)