Attached to emotion adjectives to describe the OUTWARD signs of a third person's feelings, since you cannot directly claim to know another's inner mind.
[い-adj stem / 〜たい stem] + がる (habitual) / がっている (right now)
子供は新しいおもちゃを欲しがっている。
Kodomo wa atarashii omocha o hoshigatte iru.
The child clearly wants the new toy.
欲しい (want) → 欲しがっている (showing signs of wanting).
猫は外に出たがっている。
Neko wa soto ni detagatte iru.
The cat is showing signs of wanting to go outside.
出たい (want to go out) → 出たがっている (visibly wanting to).
彼は試験を怖がっている。
Kare wa shiken o kowagatte iru.
He is acting scared of the exam.
怖い (scary/afraid) → 怖がっている (showing fear).
• Empathy rule: You avoid 彼は欲しい ('he wants') because it presumes knowledge of his mind; use 欲しがる instead. • Note the object shift: 欲しい takes が (おもちゃが欲しい), but 欲しがる takes を (おもちゃを欲しがる) because がる makes it a transitive-style verb. • がる turns an emotion adjective into a verb: 悲しい (sad, state) → 悲しがる (to act/appear sad).
The JLPT rarely asks whether you recognise a pattern — it asks which of several similar patterns fits. These are the ones がる/がっている is tested against.
〜たい / 欲しい state YOUR OWN desire directly; がる is required to describe a third person's desire from the outside.
〜そう ('looks like', 嬉しそう) is a momentary visual impression; がっている describes ongoing observable behavior over time.
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