聞く vs 効く vs 利く | Japanese Grammar

Say the word kiku out loud and you have committed to nothing — the sound きく spells at least three unrelated verbs. In speech, context sorts them out; in writing, the kanji does the work, and that is the whole point. English speakers who lean on kana (or on a dictionary's first entry) blur 聞く, 効く, and 利く together and end up writing "the medicine hears" or "please effective the way." This page pins down which kiku is which, and gives you a particle-based test that resolves most cases instantly.

聞く — hear, listen, and ask

聞（き）く is the default kiku, and it covers two English verbs at once: "hear/listen to" and "ask." Both are about sound and information reaching you, so Japanese treats them as one verb. It is transitive — the thing heard or asked is marked with を.

毎朝、音楽を聞きながら走ります。

maiasa, ongaku o kikinagara hashirimasu

Every morning I run while listening to music.

すみません、道を聞いてもいいですか。

sumimasen, michi o kiite mo ii desu ka

Excuse me, may I ask you for directions?

先生に分からないところを聞いた。

sensei ni wakaranai tokoro o kiita

I asked the teacher about the part I didn't understand.

Notice the second and third: 聞く for asking is extremely common — 道を聞く ("ask the way"), 名前を聞く ("ask someone's name"). Beginners often reach for 質問する here, which is fine but stiffer; everyday spoken Japanese just uses 聞く.

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A quick aside on 聴く: the same reading きく, but 聴 is the "listen attentively / with the whole ear" character. It is used for deliberate, appreciative listening — 音楽を聴く (savoring music), 講義を聴く (attending closely to a lecture). Casual 音楽を聞く is never wrong, but 聴く signals focus. For simply "hearing" a sound you did not seek out, only 聞く works — 物音が聞こえた ("I heard a noise"), never 聴.

効く — be effective, take effect

効（き）く means "work / take effect / be effective." It is what medicine, brakes, air conditioning, painkillers, seasoning, and advertising do. Crucially it is intransitive: the effective thing is the subject, marked with が, not を. There is no one doing the "effecting" — the medicine itself simply works.

この薬はすぐに効きますよ。

kono kusuri wa sugu ni kikimasu yo

This medicine takes effect quickly.

暑いと思ったら、クーラーが効いていなかった。

atsui to omottara, kūrā ga kiite inakatta

I thought it was hot — turns out the air conditioning wasn't working.

このスープ、生姜が効いていておいしい。

kono sūpu, shōga ga kiite ite oishii

This soup is delicious — the ginger really comes through.

That last one shows the reach of 効く: a seasoning that "takes effect" on the flavor. The unifying idea is efficacy — something producing its intended result. So "the medicine works" is 薬が効く, and ×薬を聞く ("hear the medicine") is a genuine, common error that comes straight from typing kiku and taking the first character.

利く — function well, be serviceable

利（き）く is the narrowest of the three and lives mostly in set phrases. Its core sense is a faculty, part, or arrangement working well / being usable / being available. Learn it as idioms rather than trying to translate it word by word.

Phrase	Reading	Meaning
気が利く	ki ga kiku	to be thoughtful / attentive / tactful
目が利く	me ga kiku	to have a good eye (for quality)
口を利く	kuchi o kiku	to speak / put in a word for someone
無理が利く	muri ga kiku	to be able to push oneself / handle strain
融通が利く	yūzū ga kiku	to be flexible / accommodating

彼女は本当に気が利くね。

kanojo wa hontō ni ki ga kiku ne

She's really thoughtful, isn't she?

この店は融通が利くから助かる。

kono mise wa yūzū ga kiku kara tasukaru

This shop is flexible, which is a big help.

Like 効く, 利く is intransitive and pairs with が (or を in 口を利く). There is real overlap with 効く for machinery — ブレーキがきく ("the brakes work/bite") is written both 効く and 利く, and most Japanese people would not agonize over which. But 気がきく and 目がきく are locked to 利く.

The one test that resolves most cases: the particle

You rarely need to weigh nuance if you check the particle and the meaning together.

Meaning	Verb	Particle	Frame
hear / listen / ask	聞く	を (transitive)	Xを聞く — "I hear/ask X"
take effect / work	効く	が (intransitive)	Xが効く — "X is effective"
function well / be serviceable	利く	が / を (idioms)	気が利く, 口を利く

If you are the one doing the hearing or asking, and the other thing is the direct object with を, it is 聞く. If the other thing itself is the one "working" — subject with が, no agent — it is 効く (efficacy) or 利く (a faculty in a set phrase). That single split catches the overwhelming majority of errors.

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The deep lesson goes beyond these three verbs: Japanese routinely lets homophones collapse in sound and separates them only in writing. きく, はかる (計る・測る・量る), つく, なおす (直す・治す) — the kana is ambiguous on purpose, and the kanji is where the meaning is stored. So when a kiku sentence is about efficacy or a faculty rather than sound, the correct character is 効く or 利く, and defaulting to 聞く is the error to unlearn.

A parallel family: きる — 着る, 切る, 斬る

The same "one reading, many kanji" pattern shows up with きる. 着（き）る is "wear (from the shoulders down)" and is ichidan (着ます). 切（き）る is "cut" and is godan (切ります). And 斬（き）る is a literary/archaic "cut down / slay with a blade," seen in samurai fiction and set expressions. The disambiguation logic is identical: the sound is shared, the kanji carries the meaning — you would never write 紙を着る for "cut paper."

寒いからコートを着て出かけた。

samui kara kōto o kite dekaketa

It was cold, so I put on a coat and went out.

このハサミはよく切れる。

kono hasami wa yoku kireru

These scissors cut well.

Common mistakes

❌ この薬はよく聞きます。

Wrong — 'the medicine is effective' is efficacy, not hearing. Use 効く with が.

✅ この薬はよく効きます。

kono kusuri wa yoku kikimasu

This medicine is very effective.

❌ 駅員に電車の時間を効いた。

Wrong — 'asked the station attendant' is 聞く (hear/ask), not 効く (take effect).

✅ 駅員に電車の時間を聞いた。

ekiin ni densha no jikan o kiita

I asked the station attendant the train time.

❌ 彼はとても気が効く人だ。

Wrong — 'thoughtful' is the fixed idiom 気が利く, written with 利, not 効.

✅ 彼はとても気が利く人だ。

kare wa totemo ki ga kiku hito da

He's a very thoughtful person.

❌ ワインの味が分かるなんて、口が利くね。

Wrong verb entirely — 'a good eye/palate' is 目が利く. 口を利く means 'to speak', not 'discerning'.

✅ ワインの味が分かるなんて、目が利くね。

wain no aji ga wakaru nante, me ga kiku ne

You can tell good wine — you've got a discerning palate.

Key takeaways

聞く = hear / listen / ask; transitive, takes を. This is the default kiku and covers "asking directions" too.
効く = be effective / take effect (medicine, brakes, AC, seasoning); intransitive, takes が. "The medicine works" is 薬が効く — not 聞く.
利く = function well / be serviceable, mostly in set phrases: 気が利く, 目が利く, 融通が利く, 口を利く.
The particle test: you hear/ask something (を) → 聞く; the thing itself works or a faculty is serviceable (が) → 効く / 利く.
聴く is deliberate, appreciative listening; the きる family (着る・切る・斬る) shows the same one-sound-many-kanji logic — the kanji, not the reading, stores the meaning.

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