May I: てもいいです

～てもいいです ~te mo ii desu May do; it is okay to do

Te-form + もいいです (mo ii desu) gives permission. Add か to ask for it: トイレに行ってもいいですか, "May I go to the toilet?"

Level: JLPT N5, beginner
Type: The te-form
English links: permission, modal verbs, questions

What it means

Te-form + も + いいです means "it is okay to do". Word for word, it is "even if you do it, it is good". 使ってもいいです, "You can use it."

Add か and it becomes a question: 使ってもいいですか, "Can I use it?" This is how you ask for permission, and how your students ask you in Japanese.

To say yes, people say はい、いいですよ or just どうぞ. To say no, a direct no is rare. People often say すみません、ちょっと… and let the sentence trail off. A firm rule uses てはいけません, the next point in this list.

In speech you will also hear ても大丈夫です. It means the same and is very common.

How to build it

Pattern	How it works
Te-form + もいいです (食べる → 食べてもいいです) taberu → tabete mo ii desu	Giving permission: "You may eat."
Te-form + もいいですか (入る → 入ってもいいですか) hairu → haitte mo ii desu ka	Asking for permission. 入る is Group 1, so 入って.
Te-form + も大丈夫です te-form + mo daijoubu desu	A common spoken version with the same meaning.
はい、いいですよ。 / どうぞ。 hai, ii desu yo. / douzo.	The usual ways to say yes.

Examples

トイレに行ってもいいですか。 toire ni itte mo ii desu ka. May I go to the toilet?
窓を開けてもいいですか。 mado o akete mo ii desu ka. Can I open the window?
辞書を使ってもいいです。 jisho o tsukatte mo ii desu. You can use a dictionary.
ここで写真を撮ってもいいですか。 koko de shashin o totte mo ii desu ka. Can I take a photo here?
今日は早く帰ってもいいですよ。 kyou wa hayaku kaette mo ii desu yo. You can go home early today.

How English says it

English uses modal verbs: "Can I...?", "May I...?", "Could I...?". To give permission: "You can..." or "You may...". "May" is more formal; "can" is what most people say.

English also has "Is it OK if I...?" and "Do you mind if I...?". The last one is a trap: "No" means "go ahead".

Why it can make English hard

いい means "good", so some students translate it word for word: "Is it good to open the window?"
After a modal like "can" or "may", English uses the base verb. Students sometimes add "to", as with other verbs they know.
With "Do you mind if I...?", the answer is reversed. "Yes" means "I do mind". Students who are being polite may say "Yes" and confuse everyone.

Mistakes you will hear

Is it good to open the window? Can I open the window? A word-for-word copy of 開けてもいいですか. Here いい means "okay", not "good".
May I to use a dictionary? May I use a dictionary? After "may" and "can", use the base verb. No "to".
A: Do you mind if I sit here? B: Yes, please. A: Do you mind if I sit here? B: No, not at all. Go ahead. "Yes" means "I do mind". The polite answer is "No".

In the classroom

Make a rule that students must ask in English for the small things: the toilet, a pen, the window. In my classes this does more for "Can I...?" than any worksheet.
Put three question frames on the wall: "Can I...?", "May I...?", "Is it OK if I...?". Students point to the one they used.
Give "Do you mind if I...?" its own short drill. Students must answer "No, go ahead" without thinking. It is the reflex that matters.

Practice

Try each one, then open it to check.

1. Fill the gap: 窓を開け＿もいいですか。 (Can I open the window?)

Answer: て

開ける is Group 2. Drop る and add て.
2. Ask for permission: 帰る (go home)

Answer: 帰ってもいいですか

帰る looks like Group 2, but it is Group 1, so 帰って.
3. Translate: ここに座ってもいいですか。

Answer: Can I sit here? (or: May I sit here?)

てもいいですか asks for permission. English uses "can" or "may".
4. A student writes "Is it good to use my phone?" Fix it.

Answer: Can I use my phone?

いい means "okay" here. English asks with "can".