Nasalization 비음화: Stops Become Nasals (입니다 → 임니다)

If you learn only one Korean sound-change well, make it this one. Nasalization (비음화) is the rule that turns a stop batchim — one that closes to [k], [t], or [p] — into a nasal whenever the next syllable begins with ㄴ or ㅁ. It is everywhere in ordinary speech, it is obligatory rather than optional, and it hides inside the single most common ending in the language: every formal -ㅂ니다/-습니다 sentence runs on it. Get it, and a whole layer of "foreign accent" quietly falls away. Miss it — say a hard [p] in 입니다 — and a native ear flags you as a beginner in one syllable.

The rule in one line

When a stop batchim meets a nasal (ㄴ or ㅁ), the stop becomes the nasal made at its own place of articulation. Your mouth doesn't move to a new spot — the air just reroutes through your nose. There are three tidy pairings, one per place:

Notice the pairs share a place: [k] and [ŋ]/ㅇ are both velar, [t] and [ㄴ] both alveolar, [p] and [ㅁ] both bilabial. So nasalization only changes the manner — from oral stop to nasal — while the tongue or lips stay put.

Why it happens: you can't release a stop into a nasal

Here is the physical logic, and it is worth internalizing because it makes the rule feel inevitable instead of arbitrary. A stop like [k] needs the soft palate (velum) raised, sealing off the nose so pressure builds in the mouth for a crisp burst. A nasal like [ㅁ] needs the velum lowered, so air flows out through the nose. To pronounce [ㄱ] and then [ㅁ] as spelled, you would have to slam the velum up for the stop and instantly drop it for the nasal — a fussy two-step your mouth would rather not do.

Korean simply doesn't. Anticipating the upcoming nasal, it keeps the velum lowered across the whole coda, so the batchim never gets its oral-pressure phase. It surfaces as the nasal at the same place. That is why 먹는 comes out ㄱ, which would be [k], borrows the nasality of the following ㄴ and lands on [ㅇ], the velar nasal.

먹는 → [멍는]: the [k] of 먹, meeting the ㄴ of 는, reroutes through the nose as [ㅇ].

[k] → ㄱ-type

Any batchim that closes to [k] — plain ㄱ, tense ㄲ, aspirated ㅋ, or the cluster ㄺ — becomes the velar nasal [ㅇ] before ㄴ or ㅁ.

국물 → [궁물]. And note that the following 물이 links across as [무리], so the whole thing is [궁무리].

작년 → [장년]: the [k] of 작 nasalizes to [ㅇ] before the ㄴ of 년.

한국말 → [한궁말]: the [k] of 국, meeting the ㅁ of 말, nasalizes to [ㅇ]. 박물관 works the same way — [방물관]; and any -는 attached to a ㄱ-final stem does too (읽는 → [잉는]).

[t] → ㄷ-type (a whole crowd of letters)

This group is the biggest because seven different batchim all first neutralize to a plain [t] at the end of a syllable — ㄷ, ㅅ, ㅆ, ㅈ, ㅊ, ㅌ, and even ㅎ — and once they are [t], they all nasalize the same way, to [ㄴ]. So you never have to track which original letter it was; if a syllable closes to [t] and the next one starts with ㄴ or ㅁ, you say [ㄴ].

있는 → [인는]: the ㅆ of 있 closes to [t], then becomes [ㄴ] before 는. This attributive 있는 is one of the highest-frequency words in Korean — you will say it constantly, always as [인는].

닫는 → [단는] (ㄷ → [ㄴ]). The same happens to 낱말 → [난말] (ㅌ → [t] → [ㄴ]), 옛날 → [옌날] (ㅅ → [t] → [ㄴ]), and 놓는 → [논는] (ㅎ → [t] → [ㄴ]).

[p] → ㅂ-type, and the ending that runs the language

Batchim ㅂ and ㅍ close to [p] and become [ㅁ] before a nasal. This is the pairing every learner meets on day one without realizing it, because the formal polite ending -ㅂ니다 / -습니다 (the 합니다체, or formal register) is built on exactly this collision: ㅂ + ㄴ.

입니다 → [임니다], and 뵙겠습니다 → [뵙껟씀니다], 있습니다 → 습 (ㅂ-final) becomes [ㅁ] before 니다 every single time.

감사합니다 → [감사함니다]: the ㅂ of 합 becomes [ㅁ]. You have said this phrase a hundred times — now you know why it sounds like [함니다], not [합니다].

Two nasalizations in one sentence: 박물관 → [방물관] (ㄱ → [ㅇ]) and 앞문 → [암문] (ㅍ → [p] → [ㅁ]).

Where English trips you up

English is why this rule feels unnatural at first — and, oddly, also why it shouldn't. English does the same kind of assimilation, but it hides it and treats it as optional. Say handbag fast and it becomes "hambag"; input drifts toward "imput"; pancake toward "pangcake." A stop or nasal is borrowing the place or nasality of its neighbor — the identical instinct behind 비음화.

The trap is that English also freely allows a held stop right before a nasal: "ripness," "topmost," "cheapness" all keep a clean, released [p]. So an English speaker's default is to read 입니다 as "ip-nida," releasing that ㅂ — which is precisely the error. Korean does not permit the held stop there; the ㅂ must nasalize. Unlike English, where "hambag" is a casual slur you could avoid in careful speech, Korean nasalization is fixed: 국물 is [궁물] even when you enunciate slowly, word by word.

Common Mistakes

1. Releasing the ㅂ in 입니다 / -습니다. The signature beginner slip — a crisp [p] before 니다 instead of [ㅁ].

2. Pronouncing 먹는 with a hard stop. The ㄱ can't stay a [k] in front of ㄴ; it becomes [ㅇ].

3. Reading 국물 letter by letter. A stop before a nasal never survives as a stop.

4. Treating it as optional, like the English version. Handbag → "hambag" is casual and avoidable; Korean nasalization is not. Apply it every time, even when speaking slowly and carefully — 감사합니다 is [감사함니다] at any speed.

Key Takeaways

• A stop batchim [k/t/p] becomes a nasal before ㄴ or ㅁ, at its own place: [k] → [ㅇ], [t] → [ㄴ], [p] → [ㅁ]. 국물 [궁물], 닫는 [단는], 입니다 [임니다].
• It happens because you can't hold a stop and then release it into a nasal — the velum stays down and the batchim surfaces as the matching nasal.
• The whole ㄷ-crowd (ㄷㅅㅆㅈㅊㅌㅎ) neutralizes to [t] first, so they all nasalize alike to [인는], 옛날 [옌날].
• It is baked into -ㅂ니다/-습니다: 감사합니다 [감사함니다], 있습니다 [읻씀니다] — a leftover hard [p] is an instant accent tell.
• English does the same thing (handbag → "hambag") but optionally; in Korean it is obligatory. The partner rule that turns initial ㄹ into [ㄴ] is covered in ㄹ → ㄴ after ㅁ, ㅇ, and the two-step chain in double nasalization.