Te Form - Permission

The te form, when used alongside another set phrase (listed below), can be used to ask for or grant permission.

てverb +  もいいです =  "You may do [verb]."

This can be made into a question by either changing it to ですか or providing the proper inflection. It can also be made more casual by dropping も.

　 リー：　テレビを見てもいいですか。
ホリー：　はい、いいです。

   Lee: May I watch TV?
Holly: Yes, you may.

アリス：　この苺を食べてもいいですか。
ホリー：　はい、いいです。

Alice: May I eat this strawberry?
Holly: Yes, you may.

 アヤト：　君の本を読んでいいですか。
ほりー：　いいよ。

Ayato: Can I read your book?
Holly: Sure.

  ライト：　君のノートを借りていいですか。
ほりー：　いいよ。

Laito: Can I borrow your notebook?
Holly: Sure.

To state that something is prohibited, I can use the following form:

てverb + はいけません  (or  いけない, which is not polite form)

その池で泳いではいけません。
You must not swim in that pond.

花を食べてはいけません。
You must not eat the flowers.

この水を飲んではいけません。
You must not drink this water.

This isn't something typically used in an everyday conversation because it sounds more authoritative. It's meant in the "rules" sense and would sound harsh if used with friends or acquaintances.