Japanese grammar: the difference between “のが” and ”のか”

Recently someone on Twitter was asking about the difference between “のが” (no ga) and ”のか” (no ka). I responded briefly to their post, but I wanted to give a little more detailed treatment here.

In the case of “のか”, the の is often used to an explanatory or factual feeling, similar to how it does in a sentence like this:

• 僕はアメリカ人なんです。 (boku wa amerikajin nan desu.)

Here なん actually is short for なの, and you can try and get the feel for this usage with this translation:

• The fact is that I am American.

As for the か in “のか”, it generally implies there is a question in some form, though it might be an embedded question that is not being asked to someone directly.

So now let’s look at a case where ”のか” is used:

• どこに行きたいのか分からない (doko ni ikitai no ka wakaranai)
• I don’t know where (you) want to go.

Here the “no” has a feeling of something being factual, and gives the nuance that the subject of the 行きたい is another person, not the speaker/writer. But you could drop the の here, and while it would change the nuance, it is still grammatically correct.

The above is an example of か being used to create an embedded question. A example where it is used for a direct question is:

• 君はそれで本当にいいのか？ (kimi wa sore de hontou ni ii no ka?)
• Are you really OK with that?

Note that this has a bit of a rough feeling to it.

For more information, here is an article I wrote on のか some time ago. And here is an article focusing on a few usages of の.

On the other hand, while the の in “のが” is technically the same word, it is often used as a nominalizer, which means that it turns what is a verb into a noun, so that it can be discussed in an abstract sense. The “ga” is used to mark a subject (not a topic, which is “wa”, see this article which explains the difference), and while English doesn’t really have a word for that, you can imagine the part before it in italics to give you an idea for the nuance.

• 毎日勉強するのがおすすめです。 (mainichi benkyou suru no ga osusume desu)
• I recommend that you study every day.

Here the “no” is required because without it we have the following sentence:

• 毎日勉強するがおすすめです。 (mainichi benkyou suru ga osusume desu)

Literally this sounds like “Everyday (I) will study, but It is a recommendation”. In other words, the verb is now being treated as it is actually occurring instead of being discussed in the abstract. (As a side note, I have seen cases in classical Japanese where this pattern can be used, so I am talking mostly about modern Japanese here.)

Also, notice in this case there is no question, either embedded or direct. So using のか wouldn’t really make any sense. 

Finally, let me give you two sentences so you can guess to use “のが” or ”のか” 

• 彼がどれぐらい上手な ____ 知りたいよ (kare ga dore gurai jouzau na ____ shiritai yo.)
• そんなことをいう____ 変だよ (sonna koto iu ____ hen da yo.)