We just looked at how to make questions in Japanese.

Specifically, we saw how we use ～ですか？ (and ～ますか？) at the end of polite questions and a simple rising intonation at the end of casual questions.

In this lesson, we'll be looking at a slightly different way of making casual questions: Utilizing the particle の.

Although I think it's pretty much impossible to sum up what I want to explain in this lesson using a single sentence, I'll try my best:

We place the particle の at the end of casual questions in order to show genuine interest, surprise, and/or disbelief.

Be careful! Because misreading the above explanation can get you into a lot of trouble. Specifically, what is meant by "genuine interest, surprise, and/or disbelief" might be quite different than what you're imagining.

As always, examples will teach much better than explanations.

Imagine, for example, the following situation: You've taken your friend to your favorite restaurant and demanded that they order a certain food. After they take their first bite, you can ask:

美味しい？
おいしい？
Is it good [tasty]?
Literally: "tasty / delicious?"

Compare that to the following situation:

You're at a sushi restaurant with your friend, and you see them dipping their sushi in ketchup. Being an insufferable sushi snob, you are disgusted. Still, you're a polite person, so you're not going to ridicule your barbarian friend. But you will, at the very least, ask:

美味しいの？
おいしい　の？
Is that good?
Literally: "tasty / delicious + の?"

The の shows that you're doubting whether it's good or not. You don't know the answer to this question, and you want to know what the answer is.

This is partly why I like to say that の at the end of a question shows "genuine interest." When you ask a question with の, you want an answer.

Consider the following, slightly more difficult phrase:

鶏の足っておいしいの？
とり　の　あし　って　おいしい　の？
Do chicken feet taste good?
Literally: "chicken + の + feet + って + tasty / delicious + の？"
Note: Chicken feet is a popular food in Korea, for example. It's quite rare to see in Japan, though. Also, note that って can introduce a topic much like は. We'll look at doing this in future lessons.

The speaker seems a bit doubtful that chicken feet taste good. But perhaps the listener has said that they should order it or something, so the speaker has asked this question. This question would be correct still without the の, but in that case the speaker wouldn't sound doubtful about the taste of chicken feet.

By the way, if you're confused by why 鶏の足 means "chicken feet," be sure to check out our earlier lesson on using の.

I think another way to conceptualize the meaning of の at the end of casual questions is to think of の as an indicator that the speaker has an opinion (whether positive or negative) about the thing being asked.

Or rather, the lack of の indicates that the speaker does not have an opinion one way or another (e.g. the question above about chicken feet would sound much more innocent without the の, as though the speaker has few presumptions about the taste of chicken feet).

For example...

Let's say you're speaking to a friend from Germany. You think beer might be cheap in Germany because Germany is famous for beer. Then again, you think it might be expensive because they have high-quality beer. In other words, you're not sure if beer is cheap or not! You ask:

ビール安い？
ビール　やすい？
Is beer cheap?
Literally: "beer + cheap?"

In contrast to this example, の can be used to show that the speaker wants more information about something that they've heard. They want to confirm some piece of information.

Imagine that you're sitting with a group of friends. You hear your German friend tell one of your Japanese friends that beer is cheap in Germany. Hearing this, you turn to your German friend and butt into the conversation, asking:

ビール安いの？
ビール　やすい　の？
The beer's cheap (there)?
Literally: "beer + cheap + の?"

Here the "genuine interest" is really just a desire for confirmation of some information. As mentioned earlier, it is an indication that the speaker wants a response to the question.

You're chatting with some classmates after a lesson. Some of them are planning to go study at a cafe together this afternoon. You want to go, but you're feeling a bit shy since you don't know them that well. You'd feel more comfortable if someone you knew well were going with you, so you turn to your friend, who is also in the class, and ask:

行く？
いく？
Are you gonna go?
Literally: "go?"

Consider this, instead:

Some of your classmates are talking about how they're going to a 婚活パーティー (こんかつパーティー). This is a gathering of people that are looking for a potential spouse. Kind of like a matchmaking party. You have no interest in getting married anytime soon, so you're definitely not going (also, you're shy, remember?). But then your equally shy friend says that he/she is going to join! In disbelief, you turn and say:

行くの？
いく　の？
You're gonna go (there)?(!)
Literally: "go + の?"

You're eating potato chips. You hold out the bag of chips to your friend and ask:

食べる？
たべる？
Do you want some?
Literally: "eat?"

You and your friends are at a Korean bar in Okubo (the Korean district of Tokyo). Someone has ordered chicken feet! You think, No way. Absolutely not. Then one of your friends grabs one of them and puts it onto his plate. He's gonna eat it! You turn and ask:

食べるの？
たべる　の？
You're gonna eat that?(!)
Literally: "eat + の?"

What do you think?

Are you starting to get a sense for questions ending with の？

Because that's really the key here: getting a sense for the language, which is our only hope when looking at concepts that simply do not translate well into English.

We'll see questions with and without の at the end all throughout our Japanese studies, so I wouldn't worry too much about mastering it on your first encounter. Rather, just listen to the endings of casual questions. In time, you'll get a sense for how to ask them skillfully, just like a native speaker.