-나 보다 / -(으)ㄴ가 보다: I Guess, Judging From…

When a Korean speaker sees the lights off in a friend's window and concludes "I guess they're asleep," they don't reach for 것 같다 ("it seems"). They reach for -나 보다: 자나 봐요. This is Korean's dedicated evidential guess — the conclusion you draw from external evidence in front of you, said with a slight step back from the claim, as if you're reading the situation rather than voicing an opinion. English blurs this into the same "I guess" it uses for hunches and opinions alike; Korean keeps it in its own grammatical box, and the box has a hard wall around it: you cannot use -나 보다 about your own current feelings. This page is about that box and that wall.

보다 here is not the verb "to see"

The single most useful thing to fix in your head first: the 보다 in -나 보다 is not 보다 "to look / to see." It has been bleached into a grammatical marker meaning roughly "it appears to be the case that." So 자나 봐요 does not mean "I see that they sleep" — it means "it appears they're sleeping (judging from what I can tell)." Once you stop translating the 보다, the whole construction stops feeling strange.

In both, the speaker is standing in front of some evidence — a dark window, a crowded restaurant — and reading a conclusion off it. That "reading off the evidence" is the whole meaning of the form.

The forms: verb vs. adjective vs. noun

The shape splits by what kind of word it attaches to. This split trips up nearly every learner, so it's worth memorizing as three separate slots.

Verbs take -나 보다

For an action verb in the present, attach -나 보다 straight onto the stem — no 으, no tense juggling.

Two useful sub-cases live here. Existence verbs 있다/없다 behave like verbs: 있나 봐요, 없나 봐요. And crucially, descriptive words built on 있다/없다 — 맛있다, 재미있다, 멋있다 — also take -나 보다, not the adjective ending. That's why the crowded-restaurant example above is 맛있나 봐요, never ×맛있은가 봐요.

Adjectives take -(으)ㄴ가 보다

A true adjective (a descriptive verb) takes -(으)ㄴ가 보다: -ㄴ가 after a vowel stem, -은가 after a consonant stem.

Nouns take 인가 보다

A plain noun takes 인가 보다 — the copula 이다 in its -(으)ㄴ가 shape.

Past: -았/었나 보다 for both

To push the guess into the past, put the tense on the embedded predicate with -았/었나 보다 — for verbs and adjectives. This is a favorite exam trap: the tense goes here, never on 보다.

The wall: never about your own current feelings

Here is the rule English speakers miss most often. Because -나 보다 means "I infer this from evidence," it makes no sense to aim it at something you already know directly from the inside — your own present hunger, mood, pain, or intention. You don't deduce your own hunger; you just feel it. So ×저는 배고픈가 봐요 lands as absurd, like saying "judging from the evidence, I appear to be hungry."

Swing the same sentence to yourself and it breaks. For your own state, just state it: 저는 배고파요. The wall has one narrow gate — you can use it about yourself when you're genuinely inferring, from outside evidence, a state you hadn't noticed: 나도 모르게 그 사람을 계속 생각하는 걸 보니 내가 그 사람을 좋아하나 봐 ("the fact that I keep thinking about them without realizing… I guess I like them"). But that self-detachment is a special, almost poetic move; the safe default is: -나 보다 is for other people and the outside world.

-나 보다 vs. 것 같다 vs. -는 모양이다

All three translate as "seems / must be," but they differ in where the guess comes from, and choosing wrong leaks the wrong stance.

• 것 같다 is the general-purpose, subjective guess. It can rest on evidence or on a pure gut feeling, and — unlike the other two — it can be about yourself: 저 오늘 좀 아픈 것 같아요 ("I think I'm a bit sick today") is perfectly natural.
• -나 보다 is evidential and detached: you're reading a conclusion off something observable, and you step back from it. It's colloquial and very common in speech.
• -는 모양이다 is the evidential twin of -나 보다, leaning a touch more observational and written.

The second sentence reads the empty desk and infers the absence — pure evidence, pure -나 봐요. For the full ranking of every conjecture ending by strength and by evidential source, see Degrees of Certainty.

Common Mistakes

1. Attaching the verb ending -나 to an adjective. Descriptive words take -(으)ㄴ가, not -나.

2. Using -나 보다 about your own present feeling. You don't infer your own hunger, mood, or pain.

3. Putting the tense on 보다 instead of the embedded verb. Past goes inside, as -았/었나 봐요; 보다 stays present.

4. Using 이나 보다 instead of 인가 보다 after a noun. A noun takes the copula's -(으)ㄴ가 shape, 인가.

5. Using it for your own settled plan. -나 보다 is a guess about the world, not an announcement of what you've decided to do.

Key Takeaways

• -나 보다 = an evidential guess, "I gather / it seems, judging from what I observe." The 보다 is not "to see."
• Forms split by word type: verb -나 (가나 봐요), adjective -(으)ㄴ가 (추운가 봐요), noun 인가 (학생인가 봐요), past -았/었나 for both (갔나 봐요).
• 있다-compound descriptives (맛있다, 재미있다) pattern with verbs: 맛있나 봐요.
• The wall: don't use it about your own present feelings or decided plans — those aren't things you infer.
• Versus 것 같다 (subjective, self-OK) and -는 모양이다 (more written), -나 보다 is the colloquial, evidence-driven one.