てもいい

This grammar expresses permission or allowance. It is used when you want to say that it is acceptable or permissible to do something, or that a certain situation is fine. The てもいい form follows the conjugation of the word before もいい: for verbs use the て-form, for i-adjectives use the く-form plus てもいい, for na-adjectives use で plus もいい, and for nouns simply use でもいい. It is common in casual conversation, and can be used to ask for permission (with a rising intonation) or to give permission. It carries a soft nuance of “it’s okay if…” rather than a strict rule.