-고 vs -이고
"유미는 1학년이고 소피아는 2 할년이에요."

When do I use -이고? Why is it not -고?

It doesn't seem like it has anything to do with the preceding word ending in a consonant, but I haven't found any explanation on this online.

Question

-고 vs -이고
"유미는 1학년이고 소피아는 2 할년이에요."

When do I use -이고? Why is it not -고?

It doesn't seem like it has anything to do with the preceding word ending in a consonant, but I haven't found any explanation on this online.

Answer

If you divide this sentence
: 유미는 1학년이다. 그리고 소피아는 2학년이에요.

유미는 /  1학년이다.
    S                P

1학년(first grade: just noun)  but  1학년이다(is first grade: can be predicate)

1학년이(다) + -고

ex) 먹(다) :  먹 + -고 ,      마시(다) :  마시 + -고

Answer

It is because you need to add 고 to the verb stem.  The dictionary form of '이에요/예요' is '이다(to be)'. And the verb stem of '이다' is '이'.

Here are more sample conjugation of '고'. I put  '|'  after the verb stem of each verb.

가 | 다 (to go) --> 가 (verb stem) + 고 = 가고
공부하 | 다 (to study) --> 공부하 (verb stem) + 고 = 공부하고
듣 | 다 (to listen) --> 듣(verb stem) + 고 = 듣고
이 | 다 (to be) --> 이 (verb stem) + 고 = 이고

Hope it helps!

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