Japanese automatic subjects (Omitting pronouns)

Question

In Japanese, you can often omit 私, あなた, and friends in sentences, then rely on context to get the correct subject.

However, without these words, I have no idea how to differentiate between sentences that apply to me and ones that apply to others.

For example:

らいねん　日本　へ　いく　と　言いました

Translates to (He/She) said that he will go to Japan next year, whereas:

トマト　や　りんご　を　なげた

...translates to I threw a tomato and an apple (and some other things).

What hints that the first applies to someone else? What hints that the second applies to me?

I came across this answer already, however it leaves me with more questions than answers since it says to use a "background context" that I have no idea about. It also says that assuming an omitted context is "I" will usually be safe, which has not been the case a good chunk of the time in my study material... It also says that using "I" by default in the subject sometimes "feels" wrong, which I have no intuition of.

I know I am missing something, but after much research, I still have no idea what.

Answer 1

You have to guess, based on what is most likely the intended meaning.

Let's try to translate literally as much as possible and I'll try to demonstrate what I mean...

For the two examples that you gave:

日本{にほん}に行{い}ったら日本語{にほんご}を習{なら}う

when go to Japan / will learn Japanese

トマトやりんごを投{な}げた

threw tomatoes and apples

In English, these sentences sound incomplete. But this is exactly the way to speak and write in Japanese.

So how do you make sense of something like this?

when go to Japan / will learn Japanese

Well, it's very likely that this is not the first sentence in a book or magazine article, and it's equally unlikely that it would be the beginning of a conversation. So what came before? Let's imagine... ~Woo0O0oo~~~

【You're in a classroom and the teacher points to you and says:】

マイケル君{くん}、日本{にほん}に行{い}きたいですか？
Michael, do (you) want to go to Japan?

Michael, / want to go to Japan?

はい、行きたいです。
Yes, (I) want to go (to Japan)

yes, / want to go

じゃ、日本に行{い}ったら何{なに}をしますか？
OK. What will (you) do when (you) go to Japan?

OK. / when go to Japan / what will do? 

そうですね。。。日本に行ったら。。。日本語{にほんご}を習{なら}います！
Well... When (I) go to Japan... (I) will learn Japanese!

well... / when go to Japan... / will learn Japanese!

Now, if you go back one more time and read just the grey direct-translated bits in a funny Japanese accent, you'll realize that the dialog is perfectly understandable within the context of a classroom conversation between student and teacher.

If you were to go back into the Japanese sentences and put in things like watashi-wa and anata-wa then everyone else in the classroom would be like, "Why do they keep making such a big deal about the fact that they're talking to one another?" It would sound strange and overly dramatic. But to English speakers, we're used to always having those words, and without them it feels strange.

Plus, in English we have to make our verbs and subjects agree to make sense, and if there's no subject specified to begin with, well that's not easy. Japanese doesn't make you do this agreement, so the verbs feel OK by themselves.

Back to your question though, the only thing providing a subject in these kinds of example sentences is whatever fits the most likely circumstances of the utterance. So, you have to get used to guessing at it; and the way most people speak and write, you'll probably guess correctly most of the time.

Answer 2

「来年【らいねん】日本へ行【い】くと言いました」 can mean (but is not limited to):

• I said I will go to Japan next year.
• He/she said he/she will go to Japan next year.
• I said he/she will go to Japan next year. (ie, I told someone else that he/she will go to Japan)
• You said you will go to Japan next year. (a bit hard to think of a context where this interpretation is suitable, but it's possible)

... and so on, depending on the context. It's impossible to tell the correct subject without the context. The same is true for トマトやりんごを投げた. You can't tell who threw them without the context.

In textbooks, it's not practical to always provide a long context for each example sentence, and always writing [I/you/he/she/they/we/etc] said [I/you/he/she/they/we/etc] will go to Japan is too bothersome. So you will find many example sentences that use tentative subjects like I, you, or he, just for the sake of brevity. Don't be confused by them; you need to get used to this convention.