-을 것이다

• ㄹ 것이다 (-l geosida) — after vowel or ㄹ (l)-final stems
• 을 거다 (-eul geoda), ㄹ 거다 (-l geoda) — dominant form in colloquial speech

을 (-eul, irrealis attributive suffix) + 것 (geot, “thing”) + 이다 (-ida, “to be”). Literally "it is a thing that [SUBJECT] will..."

을 것이다 • (-eul geos-ida)

1. expresses the subject's desire; typically has a future meaning, similar to English "will"

   저는 내일 시험 공부 할 거예요.

   Jeo-neun naeil siheom gongbu hal geoyeyo.

   I'm going to study for the exams tomorrow.

   저는 미국으로 갈 것입니다.

   Jeo-neun Migug-euro gal geosimnida.

   I will go to America.

   우리 어디 갈 거야?

   uri eodi gal geoya?

   Where are we going to go?

   차를 세우시지 않을 겁니까?

   cha-reul se'usiji aneul geomnikka?

   Will you not be stopping the car?

2. expresses the speaker's hypothesis or supposition, about which the speaker is reasonably confident

   언젠가 저 나무는 쓰러질 것입니다.

   Eonjen'ga jeo namu-neun sseureo-jil geosimnida.

   That tree is going to fall down some day.

   지금 이 순간에도 바람이 불고 있을 거야.

   Jigeum i sun'gan-e-do baram-i bulgo isseul geoya.

   The wind is going to be blowing this very moment.

   아마 아기가 울었을 거예요.

   Ama agi-ga ureosseul geoyeyo.

   It's probably the baby who cried.

• (colloquial pronunciation)

Colloquially, 거예요 (geo-ye-yo) is pronounced and written 거에요 (geo-e-yo). This is prescriptively considered a misspelling.

• (contrast with 겠 (-get-))

겠 (-get-) and 을 것이다 (-eul geosida) both convey the subject's desire or the speaker's hypothesis, and often have (by extension) a future sense. However, 겠 (-get-) conveys a hypothesis based on the speaker's subjective beliefs or sentiments, or based only on information perceived at the present moment. Meanwhile, 을 것이다 (-eul geosida) conveys a hypothesis based on information exterior to the speaker or beyond that perceived at the present moment.

Thus 고기가 맛있겠다 (gogi-ga masit-get-da) means that the speaker feels that the meat will taste good based on what it looks like at the moment of speaking, whereas 고기가 맛있을 거야 (gogi-ga masisseul geoya) means that the speaker has some exterior justification for believing that the meat will taste good—having previously tasted it, for instance.

The contrast extends to statements about the subject's desire. Thus 저는 미국으로 가겠습니다 (jeo-neun migug-euro ga-get-seumnida) emphasizes the speaker's subjective desire to go to America, while 저는 미국으로 갈 것입니다 (jeo-neun migug-euro gal geosimnida) implies that the speaker has not only the desire to go to America, but also some objective reason for believing that they will be able to do so.

• See -이다#Conjugation. As the subject of 이다 (ida) is always 것 (geot), which can by definition never be honored, the honorific forms do not exist.