5.2 Modals and Semi-Modals
Key Takeaways
Core modals (can, could, may, might, must, should, will, would, shall) take a bare infinitive with no to and do not inflect for person (she can, never she cans).
Separate functions: ability (can/be able to), permission (may/can), possibility (may/might/could), obligation (must/have to), advice (should/ought to), future/volition (will/would).
Deduction vs obligation: must + base form can mean strong present deduction (must be) or obligation; must have + past participle is past deduction, not past obligation.
Semi-modals have to, need to, be able to, ought to, be going to carry tense and agreement more freely and often appear as iTEP near-miss options.
Perfect modals (could have, should have, must have, might have + past participle) encode past possibility, criticism, or deduction—common advanced fill-in and error-ID targets.
5.2 Modals and Semi-Modals
Quick Answer: Modals (can, could, may, might, must, should, will, would, shall) plus semi-modals (have to, need to, be able to, ought to) are frequent iTEP Grammar targets. Match meaning (ability, permission, obligation, advice, deduction) and form (bare infinitive; perfect modals with have + past participle). Never add -s to a pure modal.
Form rules you must not break
Pure modals
- Followed by the bare infinitive: should study, not should to study, not should studying.
- No third-person -s: She can write, never She cans write.
- No do-support in questions/negatives of the pure modal itself: Can she write? / She cannot (can’t) write.
- Negation attaches to the modal: must not (prohibition) vs do not have to (no obligation)—different meanings.
Semi-modals behave more like ordinary verbs for tense and agreement:
- have to / has to / had to / will have to
- need to / needs to
- be able to (fills gaps where can has no future/perfect form: will be able to, have been able to)
- ought to (advice; close to should; keep to)
On fill-in items, options often mix should / should to / shoulds / should studying. Eliminate form failures first, then choose among remaining meaning matches.
Meaning map (what iTEP is testing)
| Function | Typical forms | Notes |
|---|---|---|
| Ability | can, could, be able to | could = past ability or polite/present possibility |
| Permission | may, can, could, might | may more formal; can common in speech |
| Possibility | may, might, could | might often slightly weaker than may |
| Strong obligation / necessity | must, have to | must often speaker authority; have to external rule |
| Lack of obligation | don’t have to, needn’t | Not the same as must not |
| Prohibition | must not, cannot, may not | must not = forbidden |
| Advice / recommendation | should, ought to | ought to rarer but tested |
| Prediction / future | will, shall (formal/offer) | shall limited; don’t overuse |
| Hypothetical / polite | would, could | Also used in conditionals |
| Strong present deduction | must + base | She must be the director |
| Strong past deduction | must have + past participle | She must have left early |
Obligation family: must, have to, should, ought to, need to
- must: strong necessity or speaker-imposed rule; also deduction in descriptive stems (That must be the main library).
- have to: external requirement (Students have to register by Friday). Past: had to. Negative don’t have to = optional, not banned.
- should / ought to: advice or mild obligation; weaker than must.
- need to: practical necessity; need not / needn’t (BrE-leaning) = no necessity.
Critical contrast for error ID and blanks:
- You must not enter = prohibited.
- You do not have to enter = entry not required. Mixing these is a classic advanced trap when the stem is about optional attendance vs banned access.
Ability and permission: can, could, be able to, may
- Present ability: can or be able to.
- Future ability: prefer will be able to (pure can has no clean future form in many textbook descriptions).
- Past ability (general): could or was/were able to.
- Past ability (one successful event): often was able to / managed to, not bare could in careful academic usage (She was able to finish the exam in time).
- Permission: May I…? formal; Can I…? everyday; past permission could / was allowed to.
Possibility and deduction
| Force | Present / future | Past |
|---|---|---|
| Strong certainty (deduction) | must be | must have been |
| Medium possibility | may / might / could be | may / might / could have been |
| Impossibility (deduction) | can’t be / cannot be | can’t have been |
iTEP trap: must have is not past obligation. Past obligation uses had to. She must have studied ≈ “I’m sure she studied.” She had to study ≈ “She was required to study.”
iTEP trap: should have + past participle = past advice not taken / mild criticism (You should have submitted earlier), not a future plan.
Perfect modals (advanced Grammar items)
Structure: modal + have + past participle
| Form | Typical meaning |
|---|---|
| could have | past possibility / ability unused |
| might have / may have | past possibility / uncertain past |
| must have | strong past deduction |
| should have / ought to have | past recommendation not followed |
| would have | hypothetical past result (often with 3rd conditional) |
| needn’t have | did something unnecessary (BrE-leaning) |
Fill-in options may show must have gone / must went / must had gone / must goes. Only must have + past participle is correct for past deduction.
Will, would, shall
- will: future prediction, willingness, promises.
- would: past of will in reported speech; polite requests; hypothetical results.
- shall: formal offers/suggestions with I/we in some varieties; rare in modern academic US stems—if present, often in fixed formal phrases.
Reported-speech echo (preview of later chapter links): “I can help” → She said she could help. Modal shifts appear in grammar items even when the full reporting chapter is separate.
Semi-modals as “escape hatches” on the exam
When a stem needs tense marking a pure modal cannot carry cleanly, the correct option is often a semi-modal:
- By next year, students will be able to access the archive.
- They had to reschedule because the lab flooded.
- Applicants need to upload transcripts before the deadline.
If all pure-modal options break form or tense, look for have to / be able to / need to.
Strategy for iTEP items
- Read the whole stem for time markers (yesterday, by then, right now) and obligation words (required, optional, forbidden, recommended).
- Name the function: ability / permission / obligation / advice / deduction / hypothetical.
- Check form: bare infinitive after pure modal; to after ought and need to / have to patterns; perfect modal needs have + past participle.
- Separate deduction from obligation when must appears.
- Eliminate options with should to, can to, musts, or double past (must had went).
Modals pack a lot of meaning into tiny words—exactly the kind of surgical structure iTEP Grammar measures. Drill contrasts (must not vs don’t have to; must have vs had to; should vs must) until recognition is automatic, then spend your seconds on harder clause items later in the set.
Which option correctly completes: “Candidates ____ upload their portfolios by Friday; late files are rejected automatically”?
have to
should to
must to
can to
“The lights are off; everyone ____ home already.” Which best expresses strong past deduction?
must go
must have gone
had to go
should go
Which sentence correctly shows that attendance is optional, not prohibited?
Students must not attend the review session.
Students must attend the review session.
Students do not have to attend the review session.
Students cannot attend the review session.
Identify the error: “By next semester, the lab can process twice as many samples per hour.” (Context: future capacity after an upgrade.)
By next semester
twice as many
per hour
can process
Sections you finish are checked off in the contents.