がる details
Examples
shows signs of feeling — turns a subjective adjective into observable third-person behavior
弟は雷をすごく怖がるんだ。
otouto wa kaminari o sugoku kowagaru n da.
My little brother gets really scared of thunder. casual
妹は友達と同じゲームを欲しがっています。
imouto wa tomodachi to onaji geemu o hoshigatte imasu.
My little sister wants the same game as her friend. neutral
彼女は人前で話すのを恥ずかしがっていた。
kanojo wa hitomae de hanasu no o hazukashigatte ita.
She was embarrassed about speaking in front of people. neutral
Formation
い-adjective stem＋がる（怖がる・痛がる・欲しがる）attaches to i-adjectiveな-adjective stem＋がる（嫌がる・不思議がる）attaches to na-adjective
Notes
Related patterns
Similar
Both license the third-person feeling talk bare 怖い forbids — 怖がっている reports observed behavior over time, 怖そうだ reads the state off a momentary appearance; がる works only on a closed set of emotion words, そう attaches to nearly any adjective.
たがる is がる bolted onto たい's stem — the same externalizing move; plain がる rides emotion adjectives (怖がる・嫌がる), たがる covers wanting-to-act.
Lookalikes
欲しがる looks like 欲しい＋がる and is exactly that — but the case flips (犬が欲しい→犬を欲しがる) and the first-person restriction lifts, so mixing the two case frames is the standard error.