According to Cambridge dictionary, the word forget can be followed by either infinitive or gerund. These are the sentences I took from the dictionary:
She would never forget seeing the Himalayas for the first time [1].
Dad's always forgetting (to take) his pills [2].
My difficulty is deciding which one to use in this context:
I have to walk back to my room when I forget [to bring/bringing] the
key. (I use the simple present to describe my routine; something I'll do if I do the other thing.)
Is there an easy way to know whether I should use infinitive-to or gerund when the verb has two possibilities like in this case? (I've learned that I must be careful to decide infinitive-to or gerund that I'll use, although it's possible to use either, sometimes it can give another different meaning).
Best Answer
Infinitive: To forget to do something is to fail to do that thing because your memory failed you. E.g., forgetting to take your pills means that you failed to take your pills.
Gerund: Your memory failed you, but you didn't necessarily fail to complete a task. E.g., "I forget meeting him." There was no task of meeting this person that you failed at; you simply don't remember the meeting that took place.
But note that "I forget meeting him" isn't particularly elegant-sounding English. People would more likely say, "I don't remember meeting him." But "I'll never forget meeting him" sounds perfectly fine.