一...就...

The 一 (jat1)...就 (zau6)... pattern is a staple of spoken Cantonese used to show that one event triggers another immediately.

1. Sentence Structure & Subject Placement
A core rule to become proficient in is that 就 (zau6) generally follows the subject of its own clause (especially for pronouns and definite nouns). However, in existential sentences or with indefinite subjects, 就 can precede the logical subject (e.g., 一落雨就好多人搭的士 - As soon as it rains, many people take taxis). The placement of the first subject depends on the sentence:

• Shared Subject: [Subject] + 一 + [Action A] + 就 + [Action B]
  Example: 佢一見到血就暈 (He faints as soon as he sees blood). If the subject is the same for both actions, you usually only say it once at the start.
• Different Subjects: [Subject 1] + 一 + [Action A], [Subject 2] + 就 + [Action B]
  Example: 佢一返嚟，我就走 (As soon as he comes back, I'll leave).
• Subject Omission (Pro-drop): Because Cantonese is a pro-drop language, you can omit the subject entirely from either or both clauses if it is obvious from context. This applies broadly to any verb, not just impersonal ones. Example: 一返到屋企就瞓 (As soon as [I] get home, [I] go to sleep).

2. Adding Emphasis
To emphasize that something happens instantly, speakers often add 即刻 (zik1 hak1) or 即 (zik1) right after 就 (zau6).
Example: 我一放工就即刻去搵你 (I'll go find you immediately as soon as I finish work).

3. Using Adjectives
This pattern isn't limited to verbs. You can use it with adjectives to describe a reaction to a state or feeling.
Example: 佢一熱就想飲凍嘢 (As soon as he feels hot, he wants to drink something cold).

4. Temporal vs. Habitual

• Temporal: A specific sequence (e.g., 'I'll call you as soon as I arrive').
• Habitual: A constant cause-and-effect (e.g., 'Whenever he sees me, he smiles'). Note that for habitual actions, Cantonese has two highly common ways to express this: you can use the '一...就...' pattern, or the verb suffix 親 (can1) using the structure [Verb] + 親 + [Object] + 都/就.... Both are very natural.

5. Tense Independence & Aspect Markers
This pattern is tense-less and relies entirely on context. It can refer to the past, present, or future. To emphasize that the first action must be fully completed before the second one triggers, the choice of aspect marker depends on the verb's meaning. For process verbs, speakers use the resultative complement 完 (jyun4) after the first verb. However, for momentary actions or state changes, the perfective marker 咗 (zo2) is perfectly natural and frequently used (e.g., 一跌咗落水就... / As soon as it fell into the water...). Crucially, momentary or achievement verbs (verbs that happen in an instant, like 見 gin3, 到 dou3, 走 zau2) do not use the completion marker 完 (jyun4). Instead, they use resultative/phase markers like 到 (dou3/dou2) or just the bare verb.
Example: 我一食完飯就去 (I'll go as soon as I have finished eating).

6. Using Resultative Complements
In addition to 完 (jyun4), you will often see other resultative complements like 到 (dou3) attached to the first verb to show that the second action triggers upon the attainment of the first.
Examples: 一食完飯就走 (Leave as soon as finishing eating), 一返到屋企就瞓 (Sleep as soon as arriving home).

7. The Negative Form
The negative form (一唔...就...) is incredibly common for habitual behaviors, meaning 'Whenever [Subject] is not / does not...'.
Example: 佢一唔開心就食嘢 (Whenever he is unhappy, he eats).

8. The 'No Time-Delay' Rule
Because this pattern implies immediate succession, learners should not insert sequence connectors like 然後 (jin4 hau6) between the clauses. The 就 (zau6) already does the job of connecting them instantly.

9. Dropping the '一'
If you drop the 一 (jat1) entirely and just rely on 就 (zau6) in the second clause, the meaning changes to a standard 'if/when' conditional (e.g., 'When/If he comes back, I'll leave'), and you lose the 'immediate succession' nuance.

10. Register
In daily conversation, 就 (zau6) is the standard connector. In formal writing, you might see 一...便 (bin6)... or 一...即 (zik1)..., but the logic remains the same.

11. Pronunciation of 一
Unlike in Mandarin where '一' undergoes tone sandhi (changing its tone depending on the following word), in Cantonese, 一 (jat1) always maintains its high level tone (Tone 1) in this pattern without undergoing any tone changes. This is a common stumbling block for learners coming from a Mandarin background.

12. Four-Character Phrases
The '一...就...' pattern is frequently used in punchy, four-character idiomatic phrases where the subject is entirely omitted. These are very common in everyday speech.
Examples: 一講就明 (Understand as soon as it's explained), 一學就識 (Learn it as soon as it's taught).

13. Imperatives and Questions
The second clause is frequently used for commands, requests, or questions, not just statements of fact.
Example: 你一到就打畀我 (Call me as soon as you arrive).