Bare Infinitive After Modal Verbs
This guide isolates a frequent structural error: adding to or an inflected verb after a core modal. It keeps the modal rule separate from let/make/help and from general infinitive choice, and shows how negatives and questions keep the same base form.
After core modal verbs such as can, could, may, might, will, shall, would, should, and must, use the base form/bare infinitive without to: “She can swim,” not “She can to swim.” The rule is specifically about modal syntax, not every environment where a bare infinitive can appear.
Key details
Choose the right form
| Question | Use | Why |
|---|---|---|
| After can/could/may/might/will/shall/would/should/must? | base form without to | Core modals select the bare infinitive. |
| Third-person subject after a modal? | still the base form | The modal carries the finite marking; the following lexical verb does not take -s. |
| A different construction such as have to? | check that construction separately | Not every modal-like expression follows the core-modal pattern. |
Quick tests
Modal complement test
Is the governing word a core modal such as can, could, may, might, will, shall, would, should, or must?
If yes: Use the base form without to.
If no: Check the complement rule for the actual verb or semi-modal.
Caveat: Check the exact construction and meaning before applying the rule mechanically.
Examples
She can finish the report today.
Can is followed by the base form finish.
They might arrive after lunch.
Might is followed by the base form arrive.
Further guidance
Agreement Boundary
The lexical verb does not take third-person -s after a modal: “She can go,” not “She can goes.”
Core Pattern
Core modals are followed by the base form without to.
Negative Question
Negatives and questions still use the same base form: “She cannot go”; “Can she go?”
Scope
Do not extend the rule to every auxiliary-like expression; have to, ought to, and semi-modals can have different patterns.
Sources and evidence
Sources are shown with the role they play in this guide. Historical or style-sensitive claims are kept within the evidence boundary described above.
- Infinitives with and without to — English Grammar Today (opens in a new tab)Cambridge University Press · Core modals take the infinitive without to/base form; distinguishes other bare-infinitive environments.
- Modality: forms — English Grammar Today (opens in a new tab)Cambridge University Press · Modal auxiliary form and complement behavior.