Warn Someone Against Doing vs. Warn Someone To Do
Cambridge documents both warn + person + against/off + -ing and warn + object + to-infinitive. Against + -ing warns the person away from an action, while the to-infinitive states an action the warning tells or prompts the person to take, often in a negative form.
Use “warn someone against doing something” to caution them not to take that action. Use “warn someone to do/not to do something” when the warning directly states the action they should take or avoid.
Key details
Choose the right form
| Context | Use | Decision |
|---|---|---|
| caution someone not to perform a named behavior | warn someone against doing | Use “against + -ing” to frame the warned-against action. |
| warning directly tells/prompts an action | warn someone to do | Use object + to-infinitive. |
| warning directly tells someone to avoid an action | warn someone not to do | Negative to-infinitive is a common form of the second pattern. |
Quick tests
Danger-action vs response-action test
Are you naming the behavior the person should avoid, or the action the warning tells them to take?
If yes: Behavior to avoid → “warn against + -ing”; prompted response → “warn + object + to/not to + verb.”
If no: Clarify which action is the danger and which is the advised response before choosing the complement.
Caveat: The patterns can describe related situations but are not mere style variants; changing the complement can change the framing.
Examples
The guide warns hikers against leaving the marked trail.
“Against + -ing” names the behavior to avoid.
The guide warns hikers to carry enough water.
The to-infinitive states the action the warning prompts.
The sign warned visitors not to enter the closed area.
A negative to-infinitive directly states the action to avoid.
Further guidance
Boundary
The two patterns can describe related situations but are not mere style variants: changing the complement can change which action is presented as the danger and which action is the recommended response.
Construction
Against + -ing frames the warned-against behavior; object + to-infinitive frames the action prompted by the warning, including common negative infinitives such as “warned them not to enter.”
Decision
Use “warn someone against doing something” to caution them not to take that action. Use “warn someone to do/not to do something” when the warning directly states the action they should take or avoid.
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.
- warn — Cambridge Dictionary (opens in a new tab)Cambridge University Press · Warn + object + to-infinitive and warn against/off + -ing patterns