jihacheoreseoneun inteones jeopsogi jal an dwaeyo.

Internet connection doesn’t work well on the subway.

Breakdown of jihacheoreseoneun inteones jeopsogi jal an dwaeyo.

• ~이: subject particle
• ~에서: location particle
• ~는: topic particle
• 안: not

Questions & Answers about jihacheoreseoneun inteones jeopsogi jal an dwaeyo.

Why does 지하철에서는 have both -에서 and -는?

Because each part does a different job.

• 지하철 = subway
• -에서 = in / at / on, marking the place where something happens
• -는 = topic marker

So 지하철에서는 means something like:

• in the subway, as for that situation...
• when it comes to being on the subway...

The -는 adds contrast or topical emphasis. It can imply something like:

• On the subway, internet access doesn’t work well
  maybe compared with other places where it does work fine.

Could I just say 지하철에서 인터넷 접속이 잘 안 돼요 without -는?

Yes, absolutely.

• 지하철에서 is a plain location statement: in/on the subway
• 지하철에서는 adds a topic/contrast feeling

So:

• 지하철에서 인터넷 접속이 잘 안 돼요 = Internet access doesn’t work well on the subway.
• 지하철에서는 인터넷 접속이 잘 안 돼요 = On the subway, internet access doesn’t work well.

The version with -는 often sounds a little more like the speaker is setting the subway apart from other places.

What exactly does 인터넷 접속 mean?