Temporal Horizon: 〜時 (When, at the time that... & aspectual timing)

Mental Model: The Time Capsule

The noun 時 (toki) fundamentally means “time”, “moment”, or “occasion”.

Grammatically, treating 時 as a standard noun makes the structure wonderfully logical: whatever clause sits before 時 acts as an adjectival modifier describing which specific moment in time you are referring to: [Modifier Clause] + とき, [Main Event]

Literally: “At the time of [Modifier], [Main Event] happens.”

The Crucial Aspect Trap: Dictionary Form vs Past Form

Here lies the single most famous grammatical checkpoint on the JLPT N5/N4: Does the verb before とき take the dictionary form or the past た-form?

The rule is based on whether the action before とき was already completed when the main event took place:

• 1. Dictionary Form (Action NOT yet completed at the moment of the main event): 日本へ行くとき、カメラを買いました。
• Meaning: Before arriving in Japan (at home or at the departure airport duty-free), I bought a camera.
• The trip to Japan had not yet occurred when the camera purchase happened!

• 2. Past た-form (Action ALREADY completed at the moment of the main event): 日本へ行ったとき、カメラを買いました。
• Meaning: After arriving in Japan (physically in Tokyo, Akihabara, or Kyoto), I bought a camera.
• The act of going to Japan was complete before the purchase occurred!

Notice that the final verb (買いました) is past in BOTH sentences! The verb before とき strictly marks relative sequence, not sentence tense.

How to Connect Across Word Classes

Connecting to とき mirrors standard noun modification:

• Verbs:
• Non-past: 寝るとき、「おやすみ」と言います。 (”When going to sleep, I say goodnight.”)
• Past: 起きたとき、雨が降っていました。 (”When I woke up, it was raining.”)

• い-Adjectives: Direct connection in plain form:
• 寂しいとき、音楽を聴きます。 (”When I feel lonely, I listen to music.”)

• な-Adjectives (The Mandatory な Bridge!): Must keep な:
• 暇なとき、本を読みます。 (”When I am free, I read books” — never *暇とき)

• Nouns (The Mandatory の Bridge!): Must use の:
• 子供のとき、よく川で泳ぎました。 (”When I was a child, I often swam in the river” — never *子供とき)

Toki vs Tara: What's the Difference?

While both can mean “when”, their communicative focus differs:

• 〜とき: Focuses on a static time frame or backdrop: “During the occasion when X happens...”

• 〜たら: Focuses on a cause-and-effect condition or trigger: “Once X happens, THEN Y immediately follows!”