Cambridge records focus on someone or something for directing attention, and standard preposition-complement grammar puts an -ing form after a preposition when the complement is an action. A to-infinitive can still appear elsewhere to express purpose, as in a larger clause about focusing in order to achieve something; that is not the same construction as focus on doing.
ReviewedEvidence2 sourcesSectionEnglish Usage
Quick answer
Use “focus on doing” when an activity is what receives your attention. “Focus to do” is not the parallel direct-complement construction.
Key details
Confusion Familygrammar-and-usage distinction
Rule Familypreposition and verb-complement pattern
TermsFocus On Doing, Focus To Do
Further guidance
Boundary
A to-infinitive can still appear elsewhere to express purpose, as in a larger clause about focusing in order to achieve something; that is not the same construction as focus on doing.
Construction
Cambridge records focus on someone or something for directing attention, and standard preposition-complement grammar puts an -ing form after a preposition when the complement is an action.
Decision
Use “focus on doing” when an activity is what receives your attention. “Focus to do” is not the parallel direct-complement construction.
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.
