When translating "I was busy yesterday," why is this incorrect?

> 昨日が忙しかったです

Isn't it the same as

> 私は昨日が忙しかったです
CC BY-SA 4.0
2017-06-08T12:05:27.937
48188
2023-08-20T20:07:30.933
2022-01-27T04:31:28.047
30454
9793
question
particle-が は-and-が
が usage in 昨日が忙しかったです
Because the subject is changed from 'I' to 'Yesterday'. Please translate it
into 「私は昨日忙しかったです」. Omitting the subject,「昨日は忙しかったです」is more natural in daily
conversations. But 「昨日が忙しかったです」 is an expression to identify the day you were
busy. So it is correct for the answer to the question 'Which day was a busy
day for you?'
CC BY-SA 3.0
2017-06-10T19:06:28.920
48280
2017-06-10T19:06:28.920
22498
48188
answer
In English, we sometimes say things like "yesterday was busy", but if you
think about it, we're not actually talking about the day itself. We don't mean
that yesterday was a particularly different kind of day than other days were
_for everybody, in general_. What we _actually_ mean is " _I_ was busy
yesterday". That is, we're talking about our own state, so really "I" should
logically be the subject of the sentence, not "yesterday".

This is why「昨日が忙しかったです」is wrong in Japanese. It actually says (literally)
"Yesterday was busy". That is, "yesterday" had a lot of things it needed to
take care of, or "yesterday" didn't get a lot of time to itself, etc.

What you actually _want_ to say is "yesterday, I was busy", or "speaking about
yesterday, I was busy". If we were to spell that out completely in Japanese,
that would be said as「昨日、私が忙しかったです」or「昨日は私が忙しかったです」(note that 私 is always the
subject (が)). However, things like 私が are usually left out if they're fairly
obvious (which they are here), so this would usually just be said
as「昨日、忙しかったです」or「昨日は忙しかったです」instead. You can see, though, that at no point
would 昨日 actually logically be the subject of anything in this sentence.
CC BY-SA 4.0
2022-11-23T18:24:01.880
97347
2022-11-23T18:24:01.880
35230
48188
answer