自動詞・他動詞 details
Examples
が for what the thing does, を for what a person does to it — the verb changes, not only the particle
あ、電気が消えた。誰か消した？
a, denki ga kieta. dareka keshita?
Oh, the light went out. Did someone turn it off? casual
窓は風で閉まったんです。私が閉めたわけではありません。
mado wa kaze de shimatta n desu. watashi ga shimeta wake de wa arimasen.
The window shut in the wind. It isn't that I closed it. neutral
お手数ですが、会議の前に資料をお集めください。資料が集まり次第、始めます。
otesuu desu ga, kaigi no mae ni shiryou o o atsume kudasai. shiryou ga atsumari shidai, hajimemasu.
Sorry to trouble you, but please gather the materials before the meeting. We will begin as soon as the materials are all in. formal
verbs with no partner at all — most verbs stand alone, and only a minority come in pairs
弟は昨日の夜、ずっとマンガを読んでたよ。
otouto wa kinou no yoru, zutto manga o yondeta yo.
My little brother was reading manga all evening yesterday. casual
祖父は毎朝、公園を三十分歩きます。
sofu wa maiasa, kouen o sanjuppun arukimasu.
My grandfather walks in the park for thirty minutes every morning. neutral
見積もりは、担当の人に頼んでおきました。
mitsumori wa, tantou no hito ni tanonde okimashita.
I have already asked the person in charge for the estimate. neutral
naming the result — ている on the intransitive member, てある on the transitive one
あれ、窓が開いてる。閉め忘れたかな。
are, mado ga aiteru. shimewasureta kana.
Huh, the window's open. Did I forget to shut it? casual
部屋の窓は、朝のうちに開けてあります。
heya no mado wa, asa no uchi ni akete arimasu.
The room's windows were opened earlier in the morning and left that way. neutral
Formation
名詞＋が＋自動詞（ドアが開く）attaches to noun phrase (schematic)名詞＋を＋他動詞（ドアを開ける）attaches to noun phrase (schematic)
Notes
落ちる／落とす — and no rule predicts the shapes. One near-exception:
a pair member ending in す is the transitive one. Most verbs have no partner
at all: 読む, 歩く and 頼む each stand on their own.
Related patterns
Similar
Both leave a finished result on stage, but てある needs a transitive verb and implies somebody arranged it (窓が開けてある), while the intransitive member denies any arranger — wind-broken glass is 割れている, and 割ってある would claim somebody broke it on purpose.
The passive keeps the doer available for a に phrase (誰かに壊された); the intransitive member removes them from the sentence altogether (壊れた), which is why Japanese reaches for it unless someone is being held responsible.
Lookalikes
ている reads two ways, and the verb's own aspect decides which — a verb of instantaneous change gives the result still holding (電気がついている, 死んでいる), a verb of ongoing activity gives the action in progress (本を読んでいる, 工事が進んでいる); nothing on the surface separates them.