How is this used differently than 이름이?
This “은 vs 이” is a rather big subject.
It will probably take a long time to master all the different connotations of them.
Still there is a basic principle that can help you in maybe 80% of the cases.
The basic rule goes like this.
- 은/는(topic marker) is for introducing a topic. The emphasis on the predicate.
- 이/가(subject marker) emphasizes the subject itself (the noun coming before 이
/가).
(they are equivalent pairs. 은 and 이 comes after an “ending consonant”, 는 and 가 after a vowel).
Ex:
- 오바마는 미국 대통령이다 → Obama 𝐢𝐬 𝐭𝐡𝐞 𝐔𝐒 𝐩𝐫𝐞𝐬𝐢𝐝𝐞𝐧𝐭.
- 오바마가 미국 대통령이다 → 𝐎𝐛𝐚𝐦𝐚 is the US president.
#1 is a simple statement with stress on the predicate “is the US president”.
#2 is saying Obama and not someone else is the president (in speech the stress will be on “Obama”).
The sentence’s connotation is like “It is Obama who is the US president”.
Ex:
- 하늘은 푸르다 → The sky 𝐢𝐬 𝐛𝐥𝐮𝐞. A general statement about the sky.
- 하늘이 빨갛다 → 𝐓𝐡𝐞 𝐬𝐤𝐲 𝐢𝐬 𝐫𝐞𝐝. Statement about a particular instance/state.
On #2, it is not a general statement anymore.
The particular sky that the speaker is looking at is red.
The emphasis is on that particular state of the sky, the subject, so 이.
Ex:
- Tom can swim → 톰은 수영할 줄 알아요
- who can swim? → 누가 수영할 줄 알아요? (누가 = 누구가 = who)
- Tom can (swim). → 톰이 (수엉) 할 줄 알아요
#1 is a general statement. 톰은… is the most natural but 톰이… can also be used.
#2 is a question specifically for the subject (who), so 누(구)가 is a must.
#3 is an answer specifically about the subject, so 톰이… is the only correct one.
In the case of 이름이 뭐예요? the speaker is specifically asking about the name, so the emphasis is on the subject and therefore 이 is used.
This rule of “what is emphasized” will get you a long way.
But there is more to them, so keep studying heeding their usags:-)