Korean guesses: -(으)ㄹ 것 같다, -겠-, -나 보다

것 같다: it seems, I think

것 같다 (geot gatda), literally “it's like the thing that …”, is the most common way to guess. It comes after a modifier, and the modifier shows the time: past -(으)ㄴ, present -는 (verbs) or -(으)ㄴ (descriptive verbs), and -(으)ㄹ for the future or a general guess.

The choice changes the meaning: (biga oneun geot gatayo) means “it seems to be raining” (you hear it now), while (biga ol geot gatayo) means “it looks like it's going to rain”. With descriptive verbs, -(으)ㄴ 것 같다 is based on what you see, and -(으)ㄹ 것 같다 is more of a guess: (masisseul geot gatayo), it looks like it will be tasty.

Word	Past	Present	Future, guess
(oda), to come	(on geot gatayo)	(oneun geot gatayo)	(ol geot gatayo)
(jota), to be good	(joatdeon geot gatayo)	(joeun geot gatayo)	(joeul geot gatayo)
(haksaengida)	(haksaengieotdeon geot gatayo)	(haksaengin geot gatayo)	(haksaengil geot gatayo)

민수 씨가 벌써 퇴근한 것 같아요.Minsu ssiga beolsseo toegeunhan geot gatayo.It seems Minsu has already left for the day.
스트레스 때문인 것 같아요.Seuteureseu ttaemunin geot gatayo.I think it's because of stress.
이번 주말에는 날씨가 좋을 것 같아요.Ibeon jumareneun nalssiga joeul geot gatayo.It looks like the weather will be nice this weekend.

Softening your opinion

Koreans use 것 같다 all the time to avoid sounding too direct, even about their own opinions and feelings: (ige deo joeun geot gatayo), I think this one is better. (geureon geot gatayo) means “I think so”, and (jal moreugesseoyo), “I'm not sure”.

At work it softens feedback: (i bubuneun jogeum sujeonghamyeon joeul geot gatayo), it might be good to change this part a little. Using it too often about yourself ( (baegopeun geot gatayo), I think I'm hungry) can sound vague, so don't overdo it.

-겠-: that must be …

-겠- reacts to what someone has just told you or what you can see, like “that must be …” or “that looks …”: (himdeulgesseoyo), that must be hard; (masitgetda), that looks delicious. For the past, use -았/었겠-: (soksanghaetgetda), you must have been upset.

It is a quick, sympathetic reaction, so it is very common in conversation, especially in casual speech with -겠다.

매일 야근해요? 피곤하시겠어요.Maeil yageunhaeyo? Pigonhasigesseoyo.You work late every day? You must be tired.
와, 사람이 정말 많겠다.Wa, sarami jeongmal manketda.Wow, it must be really crowded.

-나 보다: judging from what I can see

-나 보다 draws a conclusion from evidence in front of you, “it looks as if”, “I guess”: (saramdeuri usaneul sseugo isseoyo. Biga ona bwayo), people are using umbrellas; it must be raining. Action verbs, and take -나 보다, descriptive verbs take -(으)ㄴ가 보다, nouns 인가 보다, and the past -았/었나 보다.

It is used about other people and things you haven't experienced directly, not about your own feelings or plans. About yourself it only works for something you have just realised: (jega jalmot deureonna bwayo), I must have misheard.

거래처에서 연락이 없네요. 바쁜가 봐요.Georaecheoeseo yeollagi eomneyo. Bappeunga bwayo.We haven't heard from the client. They must be busy.
불이 꺼져 있어요. 벌써 잤나 봐요.Buri kkeojyeo isseoyo. Beolsseo janna bwayo.The lights are off. He must have gone to bed already.
저분이 새로 오신 선생님인가 봐요.Jeobuni saero osin seonsaengniminga bwayo.That must be the new teacher.

-(으)ㄹ 텐데 and -(으)ㄹ까 봐

-(으)ㄹ 텐데 (-(eu)l tende) states an expectation and prepares what comes next, often advice or concern: (jigeumeun giri makil tende jihacheollo gaseyo), the roads will be jammed now, so take the subway. At the end of a sentence it expresses a wish or regret: (sigani isseumyeon joeul tende), it would be nice if I had time.

-(으)ㄹ까 봐 (-(eu)lkka bwa) means “in case, for fear that”: (neujeulkka bwa taeksireul tasseoyo), I took a taxi in case I was late. With it says what you're worried about: (biga olkka bwa geokjeongieyo), I'm worried it will rain.

배고플 텐데 먼저 드세요.Baegopeul tende meonjeo deuseyo.You must be hungry, so please go ahead and eat.
잊어버릴까 봐 메모했어요.Ijeobeorilkka bwa memohaesseoyo.I wrote it down in case I forgot.