Is there a "default" topic when speaking in Japanese?


So I say, apropos of nothing, 「電車｛でんしゃ｝を降｛お｝ります。」 With no other context, and
no topic established, who do you assume is the person that gets off the train?
Is it me? Is it whomever I'm speaking to? Would it be hasty or incorrect to
translate this sentence as "I get off the train."? Or is it impossible to even
make a default assumption, because you have to know the situation before
understanding the sentence?

I ask because, I inevitably practise grammar and vocabulary a lot with
sentences like these, without context or topic, and I'm curious how you would
interpret them on their own.

Please use furigana for any kanji you introduce.




In this specific "(電車を)降ります" case, I know the phrase like this is actually
frequently used in a crowded train, and it means " _I_ get off!". If the
subject is " _I_ ", explicitly adding a subject ("私は降ります!") in such a case is
very unnatural in Japanese. If the subject is not "me" but someone else, I
know that people would usually say "降りる人がいます!" (lit. "There is a person
getting off!").

So, even if I have to translate this without any context, what I was doing is
to imagine the most common background context and infer the natural subject.
In this case, although it is easy to think of some exceptional examples, I
think assuming the implicit subject "I" is usually safe. Likewise, I hear
"買います" or "行きます" very often in daily conversations, and the implicit subject
is almost always "I".

But that does not mean that "I" is always the default subject, grammatically,
in Japanese language. For example, if I have to translate "2つに割れます" or
"青色に光ります" without any context at all, I feel "I" is probably not the natural
subject here.




In this specific "(電車を)降ります" case, I know the phrase like this is actually
frequently used in a crowded train, and it means " _I_ get off!". If the
subject is " _I_ ", explicitly adding a subject ("私は降ります!") in such a case is
very unnatural in Japanese. If the subject is not "me" but someone else, I
know that people would usually say "降りる人がいます!" (lit. "There is a person
getting off!").

So, even if I have to translate this without any context, what I was doing is
to imagine the most common background context and infer the natural subject.
In this case, although it is easy to think of some exceptional examples, I
think assuming the implicit subject "I" is usually safe. Likewise, I hear
"買います" or "行きます" very often in daily conversations, and the implicit subject
is almost always "I".

But that does not mean that "I" is always the default subject, grammatically,
in Japanese language. For example, if I have to translate "2つに割れます" or
"青色に光ります" without any context at all, I feel "I" is probably not the natural
subject here.

