開あく or 開あける? Here's the rule nobody gave you

Language Deep-Dive · Verbs · N3–N2

{{first_name | みんな}}さん、こんにちは ☕

You're typing in your journal app. You want to say "the door opened." You reach for the verb and freeze.

開あく or 開あける? One of these means "the door opens by itself." The other means "I opened the door." You think for ten seconds, pick one, and feel a 30% chance you got it wrong. Next sentence — "I opened the door" — and you freeze again.

You've done this before. Probably a hundred times. And somewhere in the back of your head is the suspicion that there has to be a rule, and nobody gave it to you.

There is one. Today we hand it over.

A figure in a matcha-green jacket pauses in the middle of a narrow Showa-era Tokyo alley at dusk, framed between two wooden doors. The left door drifts open on its own, spilling warm coffee-brown light onto the cobblestones. The right door is closed; the figure reaches toward its iron handle. Telephone wires cross a deep twilight sky. Vintage Japanese anime illustration style with film grain and cel-shading.

The wall isn't you. It's how this was taught.

Here's the thing most textbooks get wrong about 自動詞じどうし / 他動詞たどうし pairs: they introduce them as two columns of vocabulary, hand you 50 pairs to memorize, and call it a chapter.

Genki shows you the labels. Tae Kim explains the concept (self-move vs other-move). Anki drills them as isolated cards. None of them tell you that most pairs follow predictable sound patterns — that the shape of the verb tells you which side of the pair it is, about 80–90% of the time.

So plateau fighters end up brute-force memorizing 開あく / 開あける, 閉しまる / 閉しめる, 始はじまる / 始はじめる as separate vocabulary items. They pass the cards. They still guess in their own sentences.

The card was never the problem. The pattern under the cards was hidden.

The three patterns (covers ~80% of pairs)

There are three sound-shape patterns that decide most 自他じた pairs. We'll call them the Three Patterns. Not laws — patterns. They cover roughly 80–90% of cases, and the rest you handle with one question. More on that in a minute.

A vintage 1970s Japanese hand-illustrated reference card on aged cream paper, divided into three horizontal zones. The top zone shows a bold matcha-green calligraphic す surrounded by hand-stamped silhouettes of actions performed on objects. The middle zone shows a coffee-brown spiral surrounded by the kana まるがるわるある and silhouettes of things changing on their own. The bottom zone is split between two identical doors — one opening by itself with the kana く, one being pushed open by a hand with the kana ける. Faded red hanko ink-stamps mark the corners. Designed as a phone-screenshottable reference for the Three Patterns of Japanese transitive and intransitive verbs.

Pattern 1 — Ends in 〜す? It's transitive (他動詞たどうし).

Almost any verb ending in 〜す is 他動詞たどうし. Someone is doing it to something.

→ 出だす — take out, put out

→ 消けす — erase, turn off

→ 落おとす — drop

→ 直なおす — fix

→ 起おこす — wake up (someone)

Confidence: very high. There's basically no common counterexample at the level you're working at.

Pattern 2 — Ends in 〜まる / 〜がる / 〜わる / 〜ある? It's intransitive (自動詞じどうし).

Verbs that end in あ段だん + る — that is, 〜まる, 〜がる, 〜わる, 〜ある, 〜かる — are almost always 自動詞じどうし. Something is changing on its own.

→ 始はじまる — [something] starts

→ 集あつまる — [people] gather

→ 閉しまる — [door] closes

→ 上あがる — [something] goes up

→ 変かわる — [something] changes

Confidence: high — overwhelming for change-of-state verbs.

Pattern 3 — A 〜u / 〜eru pair? The 〜u is intransitive, the 〜eru is transitive.

When you see a verb pair where one form ends in plain 〜u and the other ends in 〜eru, the 〜u side is 自じ and the 〜eru side is 他た.

→ 開あく / 開あける — [door] opens / [I] open [door]

→ 付つく / 付つける — [light] turns on / [I] turn on [light]

→ 入はいる / 入いれる — [something] enters / [I] put [something] in

⚠️ Abunai!

Pattern 3 only applies to actual 〜u / 〜eru pairs. Don't generalize it to every verb ending in 〜eru. 焼やく is transitive and 焼やける is intransitive: same shape, opposite assignment. 壊こわす / 壊こわれる flips it too. If a pair looks like 〜u/〜eru and feels like a change-of-state pair, Pattern 3 holds. If not, ask the fallback question instead.

The fallback: "What is changing?"

The patterns cover ~80%. The remaining 20% — irregular pairs, lexical exceptions, the ones that don't fit a shape — get handled by one question:

Who or what is changing state, and is something causing it?

→ If the thing changes on its own → 自動詞じどうし + が

→ If an actor is causing the change → 他動詞たどうし + を

落おちる — something falls (自じ). 落おとす — someone drops something (他た). 出でる — something exits (自じ). 出だす — someone takes something out (他た). The question sorts them before you even look at the particle.

☝️ Chotto

Before you internalize "を = transitive," look at 道みちを歩あるく. The classic plateau-fighter trap: "transitive verbs take を, intransitive verbs take が." Partly true. But を with motion verbs marks a path, not an object. 道みちを歩あるく (walk along the road). 空そらを飛とぶ (fly through the sky). 海うみを泳およぐ (swim through the sea). The verbs are still intransitive. を is doing different work. Pick the verb first using the patterns + the fallback question. The particle follows the verb, not the other way around.

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The twelve pairs that cover most of N4–N2

Screenshot this. The 12 highest-frequency 自他じた pairs, sorted honestly by which pattern they fit.

Group	自動詞じどうし (intransitive)	他動詞たどうし (transitive)	Meaning
〜まる/〜める (Patterns 2+3)	始はじまる	始はじめる	start
	集あつまる	集あつめる	gather
	閉しまる	閉しめる	close
	変かわる	変かえる	change
Pattern 1 (〜す = transitive)	出でる	出だす	exit / take out
	落おちる	落おとす	fall / drop
	起おきる	起おこす	get up / wake (someone)
	消きえる	消けす	disappear / erase
	直なおる	直なおす	get fixed / fix
Pattern 3 (〜u / 〜eru)	開あく	開あける	open
Lexical pair (use fallback)	入はいる	入いれる	enter / put in

That's it. Twelve pairs. Four groupings. You can pin this to your phone and reference it every time you write.

☕ If you don't have an Anki source for these yet, the free Jitsuryoku Kihon deck is built around exactly these high-frequency pairs. Start there.

The ている bridge (where this pays off)

Here's the part nobody mentions when they teach 自他じた: it solves your ている problem too.

We covered this from the ている side a few weeks back (the ている form: process or change?). From the 自他じた side, it looks like this:

自動詞じどうし + ている = resultant state

The situation exists as a result of a completed change

ドアが開あいている

The door is open (currently in the state of having opened)

電気でんきが付ついている

The light is on

窓まどが割われている

The window is broken

他動詞たどうし + ている = ongoing action

Someone is actively doing something right now

ドアを開あけている

Someone is opening it right now, mid-motion

Same kanji compound, different verb, different reading of ている. The rule that decides which one is the same rule that decides 自他じた in the first place.

🎉 Yatta!

You just solved two grammar points with one rule. ✨ Every time you sort the verb correctly, the ている form sorts itself.

(Stative verbs like 知しっている, 持もっている, 住すんでいる, 結婚けっこんしている don't follow the action/state split — with these, ている reads as a state regardless of the verb's transitivity. You already use them right intuitively. Move on.)

Level up レベルアップ

Three things worth knowing if the core landed clean.

⬆️ Level up

1. The other 開ひらく is a double-agent verb. 開ひらく has a second reading, 開ひらく, and ひらく is a 自他同形動詞じたどうけいどうし (a verb whose transitive and intransitive forms are identical). 花はなが開ひらく = the flower opens (intransitive). 店みせを開ひらく = open a shop (transitive). Same form, both jobs.

This is NOT the same verb as the あく / 開あける pair you just learned. あく is intransitive-only. ひらく is the genuine double-duty one. The transitivity split runs along the reading, not the kanji. About a dozen 自他同形じたどうけい verbs exist; you learn them as exceptions, not as a pattern.

2. The 〜てある construction is the third path. ドアが開あけてある = "the door has been opened (and left in that state) intentionally, by someone." 〜てある attaches to a transitive verb + が (not を), and it carries the implication that someone left things this way on purpose. テーブルに料理りょうりが並ならべてある = the food has been laid out on the table. Critically: ドアが開あいてある is ungrammatical. 〜てある never attaches to an intransitive verb. So you now have three distinct constructions to keep separate: 自動詞じどうし+ている (resultant state), 他動詞たどうし+ている (ongoing action), 他動詞たどうし+てある (intentional resultant state). They are not a gradient. They are three different tools.

3. The 受け身うけみ substitution. ドアが開あけられている (passive of 開あける + ている) is grammatical and can describe a state, but it carries a formal, agent-salient nuance, often hinting at intrusion or reportage. For a neutral "the door is open," natives prefer the intransitive. Rule of thumb: if you'd happily skip the agent in English, use 自動詞じどうし. If you'd hint at one, use the passive.

Tofugu's full transitivity guide goes deeper on the 自他同形じたどうけい list and edge cases if you want a Saturday read.

Kanji of the Week: 開 📚

An intimate close-up at dawn of two weathered hands in matcha-green work-jacket cuffs lifting a heavy wooden crossbar free of the iron brackets of a closed wooden Japanese gate (門). A thin warm sliver of golden dawn light leaks through the central seam between the two gate leaves. The wooden bar shows decades of patina; the iron studwork on the gate sits in cool sage-green pre-dawn shadow. Vintage Showa-era anime cel-shaded illustration — the etymological story of the kanji 開 visualized as the moment a shop unlocks its doors for the morning.

☕ Kanji of the Week

開

On'yomi: カイ

Kun'yomi: あ・く / あ・ける / ひら・く

Meaning: Open. Begin. Unfold.

Key words: 開店かいてん (store opening) · 開始かいし (start, commencement) · 開ひらく (to open, double-duty) · 開あく (to open, intransitive)

Radical: 門もん (gate) + 开 (two hands lifting a bar). Picture two hands lifting the wooden crossbar off a closed gate — the gate opens.

Memory hint: A gate (門もん) with someone's hands underneath, hoisting the bar. The moment a shop unlocks its doors for the morning. That's 開.

This week's connection: The 開 family is the perfect kanji to anchor today's lesson. 開あく is the intransitive — the door opening on its own. 開あける is the transitive — you opening it. 開ひらく is the same-form double-agent we covered in Level Up. One kanji, three readings, three jobs, and now you know which is which.

New to kanji readings? Learn how on'yomi and kun'yomi work →

For more high-frequency kanji like 開, drilled with example words and readings: the Jitsuryoku Kanji Kihon deck is free and built for exactly this layer.

Renshuu Time 練習 📝

The Five-Pair Output Test — about 15 minutes.

Pick 5 verb pairs from your SRS deck, sentence-mining batch, or recent reading. (No source? Use these: 開あく / 開あける, 始はじまる / 始はじめる, 付つく / 付つける, 落おちる / 落おとす, 入はいる / 入いれる.)

For each pair, write two sentences in your journal app or on paper:

1. One using the intransitive + ている (resultant state). Example: 「窓まどが開あいている。」

2. One using the transitive + non-ている (action). Example: 「窓まどを開あけた。」

Ten sentences total. Tomorrow, read them again without looking at this issue.

(No answer key this week — this is production practice, not a quiz. The next brew will share what readers reported back.)

→ Starter: 3 pairs, 6 sentences. Pick the easiest 3 from the list above.

→ Standard: 5 pairs, 10 sentences. The intended task.

→ Challenge: 5 pairs, 10 sentences — AND add a third sentence per pair using 他動詞たどうし + 〜てある (intentional resultant state). 15 sentences total.

You'll know you did it when: the day after, at least 8 out of 10 sentences feel automatic — the verb pick happened without a deliberate pause.

🎉 Yatta!

Even if you only wrote 3 pairs and not 5, you trained the selection skill — which is the one that fails in real output. Six sentences of selection practice beats sixty Anki card reviews of recognition practice. ✨

⬆️ Level up (optional)

For each of your 5 pairs, also write the 受け身うけみ version (e.g., ドアが開あけられている) and notice when it feels right vs. when the plain intransitive is cleaner.

Last week's answers (The 6-Week JLPT Final-Push Plan): Reader replies clustered around three error patterns: pacing on long reading, register misses on near-identical grammar choices, and vocab you thought you knew. If reading was your weakest, you're in the median. If you dropped Anki new-cards to make room for post-mortem time — that's the right move.

Tiny Win

If you're at the level where 自他じた pairs trip you up, you're not behind. You hit the exact wall every plateau fighter hits — because the rule was hidden under a pile of vocabulary, not because you're slow. The wall was always going to be here. Today it has a door in it.

One thing to do this week

Reply with one word: stuck or cruising.

→ stuck — you'd still hesitate on 開あく vs 開あける in a journal entry. We'll send you the deck and the ている piece together so the pattern locks in.

→ cruising — you sorted the 12 pairs in your head while reading. Drop the Renshuu output and we'll feature the cleanest ones next week.

Either reply gets you the same thing: a real human reading your sentence and telling you what's working.

これからも一緒いっしょに頑張がんばりましょうね〜 💪

Stay connected

🎧 Catch us on the Kotoba Brew podcast — Japan through its language, one word at a time. Listen here →

Until next week,

— Kotoba Brew Editorial Desk

開く or 開ける? Here's the rule nobody gave you 🍵