Learn Korean: 하니까 VS 해서

In English, there are many conjunctions we can use to reason out. There is because, so, so that, for, etc. Korean is not behind the race and you will have to deal with a variety of connectors that are not at all interchangeable. As you know, Korean is a language of nuance so the usage of conjunction depends on what you want to imply. Two of them are –()니까 and –//여서.

The formation is kind of different. For –()니까, it depends on the last alphabet. –니까 is attached to a verb stem that ends with a vowel and –()니까 to a verb stem that ends with a consonant. On the other hand, -//여서 follows the three present tense conjugation + . Take a look at the examples below.

하다 (to do)
하니까 / 해서

맛있다 (to be delicious)
맛있으니까 / 맛있어서

Now, what’s the difference? First, we can use -()니까 when making orders or suggestions, but not –//여서.

 배고프니까 사주세요. (O)
I am hungry so buy me something.

 더우니까 밖에 나가자! (O)
I am hot so let’s go out!

심심해서 영화 보러 갈까? (X)
It's boring so shall we watch a movie?

Second, we can use –()니까 in past tense form, but not –//여서.

내가 숙제를  했으니까 TV   있어. (O)
내가 숙제를  했어서 TV   있어. (X)
I am done with all my homework so I can watch TV.

작년에 한국에  봤으니까 올해는  가도 돼지. (O)
작년에 한국에  봤어서 올해는  가도 돼지. (X)
You’ve been to Korea last year so you do not need to go this year.

Third, we use –()니까 when the speaker himself is making a reason. Hence, even if you don't add 'I', it is understandable that you are referring to yourself. -//여서 is used for general reason.

드디어 한국에   있으니까 신나.
I am excited because I can finally go to Korea.

드디어 한국에   있어서 신나.
(He/She/They) are excited because (he/she/they) can finally go to Korea.