Modal Verbs — Mood & Modality
What Is It?
Modal verbs (can, could, may, might, shall, should, will, would, must, ought to) modify main verbs to express ability, permission, possibility, or obligation.
Canonical pattern: Subject → Modal → Base Verb.
Why Use Modal Verbs?
- Precision – grades certainty (“might” < “will”).
- Flexibility – shapes polite requests (“Could you review?”).
- Policy – encodes rules (“Users must reset passwords”).
- Forecasting – outlines potential outcomes (“The patch could break tests”).
When to Choose Modal Verbs
- Security policies (“Admins must enable MFA”).
- API docs describing optional behaviour (“Clients may retry once”).
- Roadmaps projecting future work (“We will migrate to Rust”).
- UX copy asking permission (“Can we send usage stats?”).
Forming Modal Sentences
| Tense / Mood | Formula | Example |
|---|---|---|
| Present Ability | S + can + V | The CLI can parse YAML. |
| Past Possibility | S + could + V | The query could time out. |
| Obligation | S + must + V | Services must handle 503s. |
| Conditional Future | S + would + V | The UI would reload if the token expired. |
Tips for Writing with Modal Verbs
- Match modal strength to requirement (avoid “must” for optional steps).
- Use one modal per clause; skip double stacks (“may can” → invalid).
- Pair modals with base (infinitive) verbs only.
- Clarify time frame if needed (“will” vs. “shall” in legal docs).
- Check consistency across requirements tables.
Exceptions & Nuances
Shall dominates legal contracts but sounds archaic in tech blogs. Ought to conveys moral duty; reserve for advisory notes.