How-to ask/allow/deny permission to do something (て-Form VERB + もいいですか）
て-Form VERB + もいいですか as “is it okay to do VERB?”
て-Form VERB + もいい as “it is okay to do VERB”
て-Form VERB + はいけない as “it is not okay to do VERB”
This grammar construct can be broken down into the following formula:
て-Form VERB + particle も (to mean “also”) + いい (adjective that means “good”) + common phrase です + particle か (to denote a question) = “Is it also okay to do VERB?”
This grammar construct is used to ask permission to perform a certain action and operates under the implication that any given person is already inherently allowed to do certain things, such as breathe, blink, talk, etc. (hence the particle も to denote the meaning of “also” do VERB). In response to this question, the addressee can answer with て-Form VERB + もいい (”it is okay to do VERB”) to allow permission or て-Form VERB + はいけない (”it is not okay to do VERB”) to deny permission. However, because both of these expressions re-enforce the idea that the addressee has an authoritative influence upon certain actions of yours and can in turn make the addressee be overly authoritative in his/her response, て-Form VERB + ください (”please do VERB”) and ない-Form VERB + ください (”please do not do VERB”) respectively are often used instead as softer expressions. Alternatively, In the case wherein the addressee has and desires to exercise his/her authority to allow permission and seeks to use the former set of expressions, the sentence-ending particle よ can be used to soften the authoritative tone in the response.
Kono hon o karite mo ii desuka?
(May I borrow this book?)
Ee, karite kudasai.
(Yes, please do borrow it.)
Sumimasen, hochikisu o tsukatte mo ii desuka?
(Excuse me, is it okay if I use the stapler?)
Mochiron, tsukatte mo ii desuyo.
(Of course, it’s perfectly fine to use it.)
すみません 、 写真を取ってもいいですか？
Sumimasen, shashin o totte mo ii desuka?
(Excuse me, is it okay to take photos?)
Iie, shashin o totte wa ikemasen.
(No, it is not okay to take photos.)