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.
ReviewedEvidence1 sourceSectionEnglish Usage
Quick answer
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
Confusion Familygrammar-and-usage distinction
Rule Familypreposition and verb-complement pattern
TermsWarn Someone Against Doing, Warn Someone To Do
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.
Cambridge records “accuse someone of something” and specifically “accuse someone of doing something.” That supports of + -ing when the action is the alleged wrongdoing.
Cambridge records accustomed to something and gives -ing examples such as being accustomed to working or being treated in a particular way. Do not interpret the “to” after accustomed as an infinitive marker in this construction.
Cambridge distinguishes adapt to a situation or activity from transitive patterns such as adapting plans to fit new circumstances. The surface sequence “adapt … to + verb” therefore needs its grammatical structure identified before choosing an -ing form or infinitive.
Cambridge distinguishes “apologize to someone” from “apologize for something/doing something.” You can combine the two roles, as in “apologize to someone for doing something”; “to” marks the recipient while “for” marks the reason.
Cambridge distinguishes intransitive “approve of” for a favorable opinion from transitive “approve something” for official acceptance or authorization. The official-authorization sense uses transitive “approve” with an object; do not collapse that separate sense into the “approve of doing” judgment pattern.
Oxford documents the person-action pattern as be banned + from + -ing and separately documents direct-object uses of ban. The cited evidence does not support person + to-infinitive as the equivalent prohibition construction.
