것 같다 vs -나 보다: Guess or Inference | Korean Grammar

Korean has more than one way to hedge a guess, and two of the most common — -(으)ㄴ/는/(으)ㄹ 것 같다 and -나 보다 / -(으)ㄴ가 보다 — look interchangeable in translation. Both come out as "seems" or "probably" in English. But they rest on different footing. 것 같다 is your all-purpose "I think / it looks like": it works about yourself, your own plans, and even a pure hunch with no evidence at all. -나 보다 is narrower and sharper: it is a deduction about someone or something else, read off the clues in front of you. The dividing question is simple — are you the source of this information, or are you reading it off the world?

The quick answer

Use 것 같다 for any impression or softened opinion, from any basis — including a groundless feeling and including statements about yourself. Use -나 보다 only when you are inferring another person's or thing's situation from observable evidence; it cannot report your own inner state or intention. Put crudely: you can't be a detective about your own cold.

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Source test: if the guess is about your body, your mind, your plan, or is just a feeling, you are the source — use 것 같다. If you are reading external clues about someone or something else, you are inferring — use 나 보다.

The minimal pair

Same situation, two footings:

비가 오는 것 같아요.

biga oneun geot gatayo

It seems to be raining. (my impression — maybe I just feel like it)

비가 오나 봐요.

biga ona bwayo

It must be raining. (I infer it — people are coming in wet)

The first floats an impression; you might be looking out a foggy window, or you might just have a hunch. The second is a deduction with evidence behind it — the wet umbrellas by the door. 것 같다 reports how things seem to you; 나 보다 reports what you conclude about a situation you are observing from the outside.

Now flip it to yourself, and 나 보다 breaks:

저는 감기에 걸린 것 같아요.

jeoneun gamgie geollin geot gatayo

I think I've caught a cold. (fine — about myself)

옆자리 동료가 감기에 걸렸나 봐요.

yeopjari dongnyoga gamgie geollyeonna bwayo

My coworker next to me must have caught a cold. (inferred — he keeps coughing)

You would not normally say ×저는 감기에 걸렸나 봐요 about yourself, because you don't infer your own cold from outside signs — you simply feel it. That is 것 같다 territory.

것 같다 works from any basis — including none

The real breadth of 것 같다 is that it accepts any source, right down to a groundless feeling. It is the everyday Korean tool for softening an opinion or a claim:

제 생각에는 이게 더 나은 것 같아요.

je saenggageneun ige deo naeun geot gatayo

I think this one's better. (softening my own opinion)

왠지 오늘 좋은 일이 생길 것 같아요.

waenji oneul joeun iri saenggil geot gatayo

Somehow I feel something good will happen today. (pure hunch, no evidence)

That second sentence is decisive: there is no external evidence at all, just a feeling — so 나 보다 is impossible, and 것 같다 is the only option. And 것 같다 is the polite workhorse for declining or hedging about your own plans:

저 오늘은 못 갈 것 같아요.

jeo oneureun mot gal geot gatayo

I don't think I can make it today. (softly declining)

Softening "I can't come" to "I don't think I can come" with 것 같아요 is one of the most useful register moves in Korean — a blunt 못 가요 can sound curt, while 못 갈 것 같아요 leaves everyone's face intact.

것 같다 picks its modifier form by tense

Unlike 나 보다, which attaches to a plain verb form, 것 같다 takes a modifier (attributive) ending on the preceding verb, and that ending encodes tense. This is where learners most often slip:

Time	Verb form before 것 같다	Example
Present	-는	비가 오는 것 같아요 (it seems to be raining)
Past	-(으)ㄴ	비가 온 것 같아요 (it seems to have rained)
Prospective	-(으)ㄹ	비가 올 것 같아요 (it looks like it'll rain)

누가 왔다 간 것 같아요.

nuga watda gan geot gatayo

It looks like someone came by. (past — 간)

이러다가 늦을 것 같아요.

ireodaga neujeul geot gatayo

At this rate, I think we'll be late. (prospective — 늦을)

Adjectives and the copula take -(으)ㄴ: 바쁜 것 같아요 ("(he) seems busy"), 학생인 것 같아요 ("(she) seems to be a student"). See 것 같다 overview for the full paradigm.

-나 보다: the outsider's deduction

-나 보다 is built for the moment you look at evidence and draw a conclusion about someone or something outside yourself. The form splits by word class: verbs take -나 보다, while adjectives and the copula take -(으)ㄴ가 보다.

밖에 눈이 오나 봐요.

bakke nuni ona bwayo

It must be snowing outside. (people are stamping snow off their shoes)

밖이 추운가 봐요.

bakki chuunga bwayo

It must be cold out. (everyone's bundled up — adjective, so ㄴ가)

저 사람이 이 동네 사람인가 봐요.

jeo sarami i dongne saraminga bwayo

That person must be a local. (copula, so ㄴ가)

There is one honest exception worth knowing: you can aim 나 보다 at yourself when you deliberately step back and observe yourself as if from the outside — a slightly detached, often rueful tone:

저도 이제 나이가 드나 봐요.

jeodo ije naiga deuna bwayo

I guess I'm getting old too. (observing myself from outside)

But this is a marked, self-distancing move, not the default. For everyday statements about how you feel or what you intend, stay with 것 같다. For 나 보다 in depth, and its sibling 는 모양이다, see -(으)ㄴ가/나 보다 and -는 모양이다.

Common Mistakes

1. Using 나 보다 about your own feelings. You don't infer your own hunger from clues — you feel it. Use 것 같다. (Bonus: 배고프다 is an adjective, so an inference about someone else would be 배고픈가 봐요, not 배고프나 봐요.)

❌ 저는 배고프나 봐요.

jeoneun baegopeuna bwayo

Wrong — you don't deduce your own hunger; use 것 같다.

✅ 저는 배고픈 것 같아요.

jeoneun baegopeun geot gatayo

I think I'm hungry.

2. Using 나 보다 for your own plan. An intention is something you hold, not something you observe about yourself.

❌ 저 내일 이사하나 봐요.

jeo naeil isahana bwayo

Wrong — your own plan isn't an outside inference.

✅ 저 내일 이사하는 것 같아요.

jeo naeil isahaneun geot gatayo

I think I'm moving tomorrow. (if the plan itself is still uncertain)

3. Attaching -나 to an adjective. Verbs take -나 보다; adjectives take -(으)ㄴ가 보다. (And 춥다 is ㅂ-irregular: 추운가.)

❌ 날씨가 춥나 봐요.

Wrong form — an adjective needs -(으)ㄴ가 보다 (추운가), not -나.

✅ 날씨가 추운가 봐요.

nalssiga chuunga bwayo

It must be cold out.

4. Putting a dictionary form before 것 같다. 것 같다 needs a modifier ending matched to tense, not the bare 다-form.

❌ 비가 오다 것 같아요.

biga oda geot gatayo

Wrong — needs the modifier form 오는, 온, or 올.

✅ 비가 오는 것 같아요.

biga oneun geot gatayo

It seems to be raining.

Key Takeaways

것 같다 = general "I think / it seems," from any basis — a hunch, an opinion, or evidence — and works about yourself and your plans.
-나 보다 = an inference about someone or something else, read off external evidence; it can't report your own feelings or intentions (except in a marked, self-distancing tone).
Word-class split for 나 보다: verbs → -나 보다, adjectives/copula → -(으)ㄴ가 보다.
것 같다 selects its modifier form by tense: 오는 / 온 / 올 것 같다.
The test: source of the information (→ 것 같다) versus deduction from clues (→ 나 보다).

For the wider map of certainty markers, see the certainty spectrum.

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