自動詞 / 他動詞: Transitivity Pairs

Say "the door opens" and "I open the door" in English and you use the very same verb, open — only the sentence structure tells you whether someone did it. Japanese refuses to be that economical. It keeps two entirely different verbs: ドアが開く ("the door opens," by itself) and ドアを開ける ("[I] open the door"). These matched twins are called 自動詞 (じどうし, intransitive) and 他動詞 (たどうし, transitive), and Japanese has hundreds of such pairs where English merges the two ideas into one word. Learning to feel the difference is one of the great turning points in Japanese — it changes which particle you use, which verb you reach for, and even how much blame your sentence assigns.

The core split

A 自動詞 (intransitive) describes something happening on its own, with no doer in the picture. Its subject — the thing that changes — takes が.

A 他動詞 (transitive) describes someone doing something to an object. The doer is the subject (が/は) and the affected thing takes を.

Same event, two grammars. The intransitive 開く hides the agent; the transitive 開ける puts one on stage. English can only signal this with word order, so English speakers keep reaching for one verb and forcing the particles to do the work. In Japanese, you choose the verb first, and the particle follows from it.

The particle rule that flows from it

Because 自動詞 verbs have no object, they cannot take を; because 他動詞 verbs need an object, they cannot leave it out. This gives you a hard rule:

• 自動詞 → the changing thing is marked が
• 他動詞 → the changing thing is marked を

A starter set of high-frequency pairs

The endings hint at which is which but never guarantee it — that's a whole topic of its own on the transitivity pattern families page. For now, absorb the pairs as vocabulary.

The deep insight: choosing a viewpoint, not just a verb

Here is what most textbooks under-sell. Picking the intransitive or the transitive is really choosing a camera angle. The intransitive foregrounds the event and its result with no visible agent; the transitive foregrounds the doer.

Both can describe the identical smashed window. But 窓が割れた reports it as a self-standing fact, while 窓を割った pins responsibility on a person. This is why Japanese leans toward the intransitive far more heavily than English does. Where an English speaker instinctively says "I broke the plate" (subject + transitive), a Japanese speaker will very often say お皿が割れちゃった — literally "the plate broke (regrettably)" — even when their own elbow did it. Downplaying agency this way is polite, blame-diffusing, and utterly ordinary.

This grammaticalized agency-versus-spontaneity choice has no clean English equivalent, which is exactly why it feels alien at first. Once it clicks, you'll hear the difference between "it happened" and "someone made it happen" baked right into the verb.

Not every verb comes in a pair

Be careful: the pair system is common but not universal.

• Some verbs are transitive only: 食べる (eat), 飲む (drink), 読む (read), 見る (look at). There's no self-happening "it eats."
• Some are intransitive only: 行く (go), 来る (come), 寝る (sleep), 死ぬ (die), 泣く (cry). You can't "X someone" with these; to add causation you need the causative (see the causative pages).
• A handful of verbs are their own opposite depending on context, but those are rare enough to learn one by one.

A trap: を doesn't always mean transitive

One more honest wrinkle. を occasionally marks a path of motion, not a direct object — and the verb stays intransitive:

歩く, 散歩する, 飛ぶ, and 通る are intransitive; the を here means "along/through," not "the thing acted upon." So the reliable test is meaning, not just spotting を. Don't let this "path を" convince you a motion verb is transitive.

Where this leads next

The transitivity split is the foundation of two very Japanese ways of describing states. 自動詞 + ている gives a natural, agentless resultant state — 電気がついている, "the light is on" (intransitive + ている). 他動詞 + てある gives a deliberate, someone-set-it-up state — 電気がつけてある, "the light has been left on (on purpose)" (transitive + てある). You can't produce either correctly until the pairs are second nature. And when the choice is genuinely a matter of nuance, the choosing perspective page walks through the trade-offs.

Common Mistakes

Key Takeaways

• 自動詞 (intransitive) = happens by itself, subject takes が; 他動詞 (transitive) = someone does it, object takes を.
• The verb decides the particle — choose the verb that matches whether there's a doer.
• The choice is a viewpoint: intransitive hides the agent (窓が割れた), transitive names one (窓を割った), and Japanese leans intransitive to soften blame.
• Not all verbs pair up, and a "path を" can appear on a motion verb without making it transitive.