-히

하 (-ha-) +‎ 이 (-i, adverb-deriving suffix).

• (SK Standard/Seoul) IPA^(key): [çi]
• Phonetic hangul: [히]

히 • (-hi)

1. -ly; an adverb-deriving suffix, attaching primarily to adjectives formed by the light verb 하다 (hada).

   ‎솔직하다 (soljikhada, “to be honest”) + ‎히 (-hi) → ‎솔직히 (soljikhi, “honestly”)

   ‎깔끔하다 (kkalkkeumhada, “to be neat”) + ‎히 (-hi) → ‎깔끔히 (kkalkkeumhi, “neatly”)

Generally speaking, 히 (-hi) is used for adjectives formed by 하다 (hada). 이 (-i) is used for all non-하다 (hada) adjectives. 게 (-ge) can be used for both and is often interchangeable with other suffixes. However, there are exceptions.

• Some 하다 adjectives lose the consonant ㅎ (-h-) entirely, taking 이 (-i) instead. In the prescriptive standard of Seoul Korean, this happens in the following situations:
  • If the non-하다 element ends in ㅅ (s), 이 is always used.

    ‎깨끗하— (kkaekkeutha-, “to be clean”) + ‎이 (-i) → ‎깨끗이 (kkaekkeusi, “cleanly”)

  • If the non-하다 element ends in ㄱ (g), 이 is often used.

    ‎굵직하— (gukjikha-, “to be stout”) + ‎이 (-i) → ‎굵직이 (gukjigi, “stoutly”)

• A few 하다 adjectives only use 게 (-ge) and do not use 히 (-hi). There is no predictable rule for them.

  ‎행복하— (haengbokha-, “to be happy”) + ‎게 (-ge) → ‎행복하게 (haengbokhage, “happily”)

• For a few adverbs, the 히 form is prescriptively used despite being derived from non-하다 adjectives. However, most of these words have fallen out of use in spoken Korean. Note also that certain adverbs which originate as contractions of longer adverbs may use 히 even when there is no corresponding 하다 adjective for the contraction, and that some Sino-Korean adverbs with 히 have lost their adjectival counterpart entirely.
• In practice, many Seoul speakers will uniformly use 히 for all adverbs where the corresponding 하다 adjective remains current in the language.