When should I use は?


> あれは何ですか what’s that?  
>  今何時ですか what time is it now?

I learnt these two sentences from a Japanese learning app. I am confused why
the first sentence uses は whereas the second doesn’t. The English translations
are both in the form “what is...?”




The first point to make is that the first sentence can work without the は
(though it’s slightly informal to drop it) and the second sentence can work
with a は (though it’s more common/natural to not have it).

That said, there is probably a difference in the grammar, which is that あれ is
functioning as the topic in the first sentence, while 今 is functioning more
adverbially in the second sentence (similar to how the “right now” in “what
time is it _right now_ ” works). Perhaps due to this, usage of は in the second
sentence feels like it has some sort of extra nuance, like contrast. That
said, in a very formal context I feel like people would include it regardless
(perhaps as a form of
[hypercorrection](https://en.m.wikipedia.org/wiki/Hypercorrection)?).




The first point to make is that the first sentence can work without the は
(though it’s slightly informal to drop it) and the second sentence can work
with a は (though it’s more common/natural to not have it).

That said, there is probably a difference in the grammar, which is that あれ is
functioning as the topic in the first sentence, while 今 is functioning more
adverbially in the second sentence (similar to how the “right now” in “what
time is it _right now_ ” works). Perhaps due to this, usage of は in the second
sentence feels like it has some sort of extra nuance, like contrast. That
said, in a very formal context I feel like people would include it regardless
(perhaps as a form of
[hypercorrection](https://en.m.wikipedia.org/wiki/Hypercorrection)?).

