Cambridge explicitly identifies the “to” in look forward to as a preposition and documents noun or -ing complements. The sequence “to do” is not the normal complement of look forward to because the construction does not contain infinitival to.
ReviewedEvidence1 sourceSectionEnglish Usage
Quick answer
Use “look forward to doing,” not “look forward to do.” In this expression, “to” is a preposition and the following verb takes the -ing form.
Key details
Confusion Familygrammar-and-usage distinction
Rule Familypreposition and verb-complement pattern
TermsLook Forward To Doing, Look Forward To Do
Further guidance
Boundary
The sequence “to do” is not the normal complement of look forward to because the construction does not contain infinitival to.
Construction
Cambridge explicitly identifies the “to” in look forward to as a preposition and documents noun or -ing complements.
Decision
Use “look forward to doing,” not “look forward to do.” In this expression, “to” is a preposition and the following verb takes the -ing form.
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.
