Tensification (경음화)
After stop consonants ㄱ, ㄷ, ㅂ, plain consonants ㄱ/ㄷ/ㅂ/ㅅ/ㅈ become tense (된소리).
Tensification (경음화) is the rule that turns plain consonants into their tense counterparts in specific environments. The main trigger is when the previous syllable ends in one of the 'stop' final consonants ㄱ, ㄷ, or ㅂ. Following the stop, any plain ㄱ / ㄷ / ㅂ / ㅅ / ㅈ becomes tense: ㄲ / ㄸ / ㅃ / ㅆ / ㅉ.
Example: 학교 (school) is spelled hak + gyo but pronounced hak + kkyo. The ㄱ at the end of 학 triggers tensification on the next ㄱ. Native speakers do this automatically and do not consciously notice the change, but for learners it is one of the gaps between 'reading speed' and 'listening speed'. After enough exposure, you will start producing tense consonants automatically when speaking — at which point your Korean will sound noticeably more native.
경음화 — Tensification Rule
When a syllable ends in ㄱ, ㄷ, or ㅂ (unreleased stop), the following consonant ㄱ/ㄷ/ㅂ/ㅅ/ㅈ becomes its tense counterpart: ㄲ/ㄸ/ㅃ/ㅆ/ㅉ. This makes the sound feel more 'tight' or 'sharp'.
경음화 — Common Patterns to Remember
경음화 is very common in compound nouns, place names, and everyday words. Once you recognize the pattern, you'll hear it everywhere: 입구[입꾸], 국밥[국빱], 합격[합껵].