Nasalization (비음화)
Stop consonants ㄱ, ㄷ, ㅂ become nasal ㅇ, ㄴ, ㅁ before nasal consonants ㄴ or ㅁ.
Nasalisation (비음화) changes the stop consonants ㄱ, ㄷ, ㅂ into the nasals ㅇ, ㄴ, ㅁ when they meet a following nasal consonant ㄴ or ㅁ. The most common context where you will encounter this is the formal verb ending -ㅂ니다/습니다, which is always pronounced -ㅁ니다/슴니다 even though it is always spelled with ㅂ.
Example: 학년 (school year) is spelled hak + nyeon but pronounced hang + nyeon. The ㄱ at the end of 학 changes to ㅇ before the ㄴ of 년. Similarly 합니다 sounds like 'ham-ni-da', not 'hap-ni-da'. This rule is one of the most consistent in Korean — it applies essentially every time you have a stop final consonant followed by a nasal initial. Pay attention to formal-style sentences in particular, since they trigger nasalisation in almost every verb.
비음화 — Nasalization Rule
When ㄱ, ㄷ, or ㅂ is followed by a nasal consonant ㄴ or ㅁ, the stop consonant changes to the corresponding nasal: ㄱ→ㅇ, ㄷ→ㄴ, ㅂ→ㅁ.
비음화 — The Three Pairs
Remember these three pairs: ㄱ(g/k) → ㅇ(ng), ㄷ(d/t) → ㄴ(n), ㅂ(b/p) → ㅁ(m). All three become the nasal that shares the same place of articulation in the mouth.
How It Works
비음화 is assimilation: a consonant changes to match a neighbour. When a stop ㄱ, ㄷ or ㅂ is followed by a nasal ㄴ or ㅁ, the stop becomes nasal too. The pairs are fixed and easy because each stop becomes the nasal made in the same part of the mouth: ㄱ→ㅇ, ㄷ→ㄴ, ㅂ→ㅁ.
The mechanism is physical. To make a nasal you lower the soft palate so air escapes through the nose. To make a stop you keep it raised so air is blocked completely. Shifting between those two positions mid-word is effortful, so speech takes the shortcut of lowering the palate early — which converts the stop into the nasal sharing its place of articulation. ㄱ and ㅇ are both made at the back of the mouth, ㄷ and ㄴ both at the teeth ridge, ㅂ and ㅁ both at the lips.
So 국물 becomes [궁물] and 입니다 becomes [임니다]. Notice that 입니다 is the formal sentence ending you will hear constantly in announcements and news broadcasts — and it is essentially never pronounced as written. 한국말 → [한궁말] and 박물관 → [방물관] show the same ㄱ→ㅇ shift inside familiar words.
Where You'll Hear It
The formal verb ending -습니다 / -입니다 is the highest-frequency site for this rule. Every news anchor, every subway announcement, every formal self-introduction uses it, and every one of them says [-슴니다] / [-임니다]. A learner who pronounces the ㅂ will sound immediately foreign in exactly the register where sounding polished matters most.
Food and place vocabulary supplies the rest. 국물 ('broth') comes up whenever you discuss soup, which in Korean cuisine is often. 박물관 ('museum') appears on every tourist map and subway exit sign. 한국말 ('the Korean language') is something you will say about yourself constantly while learning.
There is a practical listening consequence too. Learners searching a dictionary for a word they heard as [궁물] will find nothing, because the entry is 국물. Knowing the rule lets you work backwards from sound to spelling, which is a skill you need long before your vocabulary is large enough to guess from context.
Cultural & Language Note
비음화 is why the extremely common 입니다 is pronounced 'imnida' rather than 'ipnida'. Because 입니다 appears in nearly every formal sentence a learner will hear, getting this one rule right immediately improves how natural your formal speech sounds. The change is purely mechanical: a stop consonant cannot survive next to a nasal, so it becomes the matching nasal.
Common Mistakes to Avoid
Saying 'ip-ni-da' is the most common single pronunciation error among beginners, and it appears in the sentence you will use most often. The three pairs are fixed: ㄱ becomes ㅇ, ㄷ becomes ㄴ, ㅂ becomes ㅁ. Learners also forget it applies inside words, not just at word boundaries — 국물 is 'gungmul', not 'guk-mul'.
How to Practice This Lesson
Memorise the three pairs as pairs, not as six separate facts: ㄱ→ㅇ, ㄷ→ㄴ, ㅂ→ㅁ. Say them as a chant a few times; the correspondence is regular enough that this genuinely works.
Then attack the highest-value item first. Practise -입니다 and -습니다 until [임니다] and [슴니다] are automatic, because these two endings alone will account for most of your exposure to the rule. Say a full self-introduction aloud — 저는 학생입니다 — and check that you are not pronouncing the ㅂ.
Finally, train the reverse direction. Have someone read 궁물, 방물관, 한궁말 aloud and write down the correct spelling. Going from sound back to spelling is the skill you need for dictionary lookup, and it is rarely practised.