Grammar
-아/어지다
Meaning
Beginner-a/eojida
Attached to a descriptive verb (an adjective), -아/어지다 turns a state into a change of state: 높다 'be high' becomes 높아지다 'rise', 시원하다 'be cool' becomes 시원해지다 'get cooler', 가능하다 'be possible' becomes 가능해지다 'become possible'. What comes out is an ordinary verb, which is how Korean says 'get ~er' without a separate word for 'become'.
Form
Take the stem and apply the same -아/어 vowel rule as the polite -아요/어요 form, then add 지다: stems whose last vowel is ㅏ or ㅗ take -아지다 (많다 → 많아지다), all others take -어지다 (넓다 → 넓어지다), and 하다 adjectives become -해지다 (시원하다 → 시원해지다). The result conjugates as a regular verb: 시원해집니다, 시원해졌다. On an action verb the same ending gives a resultative reading instead (만들다 'make' → 만들어지다 'be made').
Examples
가을이 되면 날씨가 시원해집니다.
When autumn comes, the weather becomes cool.
Common mistakes & nuance
Two cautions. Do not stack it on 되다: 되어지다 doubles up a change that 되다 already carries and is treated as an error, so write 개선됐다, not 개선되어졌다. And it is not a synonym of -게 되다 — -아/어지다 describes the thing itself changing degree (물가가 높아졌다 'prices have got higher'), while -게 되다 reports arriving at a situation, usually through outside circumstances, and normally sits on an action verb rather than an adjective.
Similar grammar
- -게 되다
-게 되다 reports that a situation came about, usually through circumstances outside the subject's control, and attaches to action verbs. -아/어지다 attaches to adjectives and says the quality itself shifted — for a state getting stronger or weaker, -아/어지다 is the natural choice.
- -되다
-되다 makes a verb out of a Sino-Korean noun and states that the action was carried out or the state came about (개선되다 'be improved'). -아/어지다 attaches to an adjective already in the language and reports it changing degree (좋아지다 'get better'). News sentences often carry both.