Be Certain To Do vs. Certain Of Something
Cambridge directly records certain + to-infinitive and certain of + noun, allowing the two attested structures to be compared without claiming they are freely interchangeable.
Use “certain to do/be…” for something expected or sure to happen. Use “certain of something” when certainty is about a fact, result, or object of belief.
Key details
Choose the right form
| Meaning / situation | Construction | Decision |
|---|---|---|
| expected or sure event | certain to + verb | express confidence that an event will occur |
| certainty about a fact/object | certain of + noun/-ing | name what the person is sure about |
Quick tests
Event-or-object test
Are you predicting an event as sure/expected, or naming the fact or thing someone is sure about?
If yes: Use “certain to + verb” for the event.
If no: Use “certain of + noun/-ing” for the object of certainty.
Caveat: The constructions overlap in broad idea but are not word-for-word substitutes.
Examples
The change is certain to attract attention.
The infinitive describes the event expected to occur.
She is certain of the answer.
“Of” introduces what she is sure about.
They are certain of having followed the instructions.
An -ing phrase can name the object of certainty after “of.”
Further guidance
Core difference
Cambridge documents certain + to-infinitive and certain of + noun as standard patterns with different complement roles.
Style Boundary
Use the construction that matches the intended grammar: infinitive after certain for the expected action/state, and of before the object or fact of certainty.
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.
- Certain (opens in a new tab)Cambridge University Press · Direct learner-dictionary evidence for certain of + noun and certain + to-infinitive.