Breakdown of keisatsu wa musen o tsukau.
Questions & Answers about keisatsu wa musen o tsukau.
- は marks 警察 as the topic: As for the police, ...
- を marks 無線 as the direct object of the verb 使う: it is the thing being used.
So the structure is:
- 警察 は = as for the police
- 無線 を = radio / wireless communication
- 使う = use
は and が are both important particles, but they do different jobs.
In this sentence, は is natural because the sentence is making a general statement about the police:
- 警察は無線を使う。
Police use radios. / As for the police, they use radios.
If you used が instead:
- 警察が無線を使う。
it would sound more like you are specifically identifying the police as the ones who use radios, perhaps in contrast with someone else.
Very roughly:
- は = talking about a topic, often in a general way
- が = identifying or emphasizing the subject
