What is the use of the 'は' particle in this sentence?


The sentence is 'あなたには僕が見えるか？', which supposedly translates to 'Can you see
me?'.

I'm confused about the usage of the ’は’ particle here. Since there is already
the ’が’ particle to indicate that 僕 is the subject and the ’に’ particle to
indicate that あなた is the passive agent, what is the use of the ’は’ particle?

*The sentence is taken from the lyrics of the song 'Unknown Mother Goose'.




This は is a topic marker. A topic and a subject are related but different
concepts in Japanese, and "double subject" sentences are not uncommon (see
[this](https://eastasiastudent.net/study/topic-prominent/)).

Here are two sentences where different words are topicalized. Both sentences
translate as "Can you see me?" (or "Am I visible to you?") into idiomatic
English, but I added super-literal translations to show the difference.

> あなたには僕が見えるか？  
>  _As for you_ , am I visible?
>
> 僕はあなたに見えるか？  
>  _As for me_ , (am I) visible to you?




This は is a topic marker. A topic and a subject are related but different
concepts in Japanese, and "double subject" sentences are not uncommon (see
[this](https://eastasiastudent.net/study/topic-prominent/)).

Here are two sentences where different words are topicalized. Both sentences
translate as "Can you see me?" (or "Am I visible to you?") into idiomatic
English, but I added super-literal translations to show the difference.

> あなたには僕が見えるか？  
>  _As for you_ , am I visible?
>
> 僕はあなたに見えるか？  
>  _As for me_ , (am I) visible to you?

