Forget Doing vs. Forget To Do
“Forget + -ing” concerns whether an earlier event remains in memory. “Forget + to-infinitive” means the intended action was not remembered and therefore may not have been done.
“Forget doing” concerns memory of a past event. “Forget to do” means fail to remember to perform the action.
Key details
Choose the right form
| Meaning / situation | Form / construction | Decision |
|---|---|---|
| memory of an earlier event or action | forget + -ing | Use “forget doing” when the question is whether a past event remains in memory. |
| failure to remember an intended action | forget + to-infinitive | Use “forget to do” when the action was not remembered at the needed time. |
Quick tests
Meaning / construction test
Is the sentence about remembering an event that already happened?
If yes: Use “forget” plus the -ing form.
If no: Use “forget to” plus the infinitive when the issue is failing to remember an intended action.
Caveat: The constructions differ in time relation and meaning; do not choose only by which form sounds shorter.
Examples
I will never forget meeting her for the first time.
The meeting is a past event being remembered.
I forgot to attach the file.
The intended action was not remembered.
Do not forget to lock the door.
The infinitive refers to an action that still needs to be remembered.
Further guidance
Boundary
The two patterns differ in what is forgotten: a memory of an event versus the need to carry out a task.
Infinitive Pattern
Use forget + to-infinitive when someone fails to remember to perform an action.
Ing Pattern
Use forget + -ing for losing or lacking a memory of an event or experience; “never forget doing” means the memory remains.
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.
- Forget — Cambridge Dictionary (opens in a new tab)Cambridge Dictionary · Dictionary evidence for forget complementation and for the irregular forms forget, forgot, forgotten; Cambridge American usage also records forgot as a past-participle variant.