明日が/明日は, what's the difference?


I know it's a complicated grammar concept that even Japanese don't fully get,
but I'd like to know what's the difference between

明日は火曜日です and 明日が火曜日です

They way I understand it, in the second sentence you're indicating that
tomorrow, and not any other day, is Tuesday. And in the first one, you're
indicating that tomorrow is Tuesday, and not any other day.

Would this be correct?




The former (明日は…) is an answer to a question "What day is tomorrow?" while the
latter (明日が…) is that to "When is Tuesday?".

Edit: "Topic" stands for imformation that's suggested in the preceding
context, so when we see 明日は…, we can imagine some contexts that include "明日"
e.g. "明日は何曜日？". On the other hand, 明日が火曜日 is inversion of 火曜日は明日, and we can
think of one that includes 火曜日 e.g. "火曜日はいつ？".

