Transitive-Intransitive Pairs

In Japanese, many verbs share a root but have different endings to indicate their 'direction.' This is a fundamental concept for building natural sentences.

1. Transitive Verbs（他動詞）
These verbs describe an action performed by someone or something onto an object. While they can take a direct object, the object is often omitted if understood from context.
Example: 窓（まど）を開（あ）ける (To open the window).

2. Intransitive Verbs（自動詞）
These verbs describe a change that happens to the subject, a state that exists, or an action performed by the subject alone. They do not take a direct object.
Example: 窓（まど）が開（あ）く (The window opens).

3. Describing States and Actions: ている vs. てある
The choice of verb type changes the nuance significantly:

• Intransitive + ている: For verbs of change, it describes a natural state or the result of a change (e.g., 窓（まど）が開（あ）いている - The window is open). For action verbs, it describes an ongoing action (e.g., 走（はし）っている - is currently running).
• Transitive + ている: Describes an ongoing action OR a resultant state maintained by the agent. (e.g., 窓（まど）を開（あ）けている - Someone is currently opening the window, or Someone has the window open).
• Transitive + てある: Describes a state intentionally created by someone, often as the result of a preparation (ておく). The object marker を often changes to が (e.g., 窓（まど）が開（あ）けてある - The window has been opened [intentionally]), but を is perfectly grammatical if the sentence focuses on the agent's preparation (e.g., 換気（かんき）のために窓（まど）を開（あ）けてある - I have opened the window for ventilation). Crucially, てある can ONLY be used with volitional verbs (意志動詞 - verbs describing intentional actions). Transitive verbs describing unintentional actions cannot be used with てある unless done on purpose. For example, 財布（さいふ）が落（お）としてある sounds like the wallet was dropped intentionally (e.g., as a trap), not by accident.
• Intransitive + てある: This combination is ungrammatical (e.g., 窓（まど）が開（あ）いてある is incorrect).

4. Common Morphological Patterns
While you must learn each pair, there are reliable patterns. Note that not all verbs have a corresponding pair; some exist only as transitive or intransitive. Additionally, some verbs are ambitransitive（自他動詞 - じたどうし）, meaning they act as both without changing form (e.g., 開（ひら）く, 閉（と）じる).

• 〜う-sound (Intransitive) / 〜える-ending (Transitive): 開（あ）く / 開（あ）ける (to open), 付（つ）く / 付（つ）ける (to attach/turn on).
• 〜ある (Intransitive) / 〜える (Transitive): 閉（し）まる / 閉（し）める (to close).
• 〜れる (Intransitive) / 〜す (Transitive): 壊（こわ）れる / 壊（こわ）す (to break).
• 〜る (Intransitive) / 〜す (Transitive): 直（なお）る / 直（なお）す (to fix).
• 〜える (Intransitive) / 〜だす (Transitive): 出（で）る / 出（だ）す (to leave/put out).

5. The Motion Exception
Some intransitive verbs of motion (like 散歩（さんぽ）する - to stroll, or 飛（と）ぶ - to fly) can use the particle を to indicate the path or space through which the subject moves (e.g., 公園（こうえん）を歩（ある）く - walk through the park).