一定要/一定係

Must Do vs. Must Be

Level 3Sounds Like jat1 ding6 jiu3 / jat1 ding6 hai6

In English, the word 'must' covers two different meanings: 'You must go' (obligation) and 'It must be raining' (deduction). Cantonese usually separates these into two patterns: 一定要 (jat1 ding6 jiu3) for things you are required to do, and 一定係 (jat1 ding6 hai6) for things you are sure are true.

How It Works

Cantonese learners often fall into the 'English Must Trap' by using one word for both concepts. To avoid this, always ask yourself: 'Am I giving an order/requirement, or am I making a logical guess?'

1. Expressing Obligation with 一定要
This pattern combines 一定 (definitely) with 要 (must/need). It functions as a command or a statement of necessity.

  • 你一定要食藥。 (You must take your medicine.)
  • 我聽日一定要返工。 (I must go to work tomorrow.)

2. Expressing Certainty with 一定係
This pattern combines 一定 with the copula 係 (to be). It indicates that based on what you see or know, something is definitely the case.

  • 佢咁耐都未返，一定係蕩失路。 (He hasn't returned for so long; he must be lost.)
  • 呢把聲一定係陳生。 (This voice must be Mr. Chan.)

3. Negation Nuances
Be careful with the placement of 唔 (m4):

  • 唔一定 (m4 jat1 ding6): Not necessarily (e.g., 唔一定係佢 - It's not necessarily him).
  • 一定唔 (jat1 ding6 m4): Definitely not (e.g., 佢一定唔會嚟 - He definitely won't come).

Examples (5)

  1. 你聽日一定要準時呀。

    You must be on time tomorrow.

    Word by Word: You tomorrow definitely must on time [particle].

    Here, 一定要 (jat1 ding6 jiu3) expresses a requirement or obligation for the listener.

  2. 佢咁叻，一定係第一名。

    He is so smart, he must be first place.

    Word by Word: He so smart, definitely is first place.

    一定係 (jat1 ding6 hai6) is used here because the speaker is making a logical conclusion based on the person's intelligence.

  3. 我一定要喺十二點前返到屋企。

    I must get home before twelve o'clock.

    Word by Word: I definitely must at twelve o'clock before return-reach home.

    This expresses a personal necessity or a rule the speaker must follow.

  4. 出面咁大雨，佢一定係喺房度。

    It's raining so hard outside, he must be in his room.

    Word by Word: Outside so big rain, he definitely is at room [location marker].

    The speaker is deducing the person's location based on the weather, so 一定係 (jat1 ding6 hai6) is used.

  5. 你一定要試吓呢個點心！

    You definitely must try this dim sum!

    Word by Word: You definitely must try [bit] this [classifier] dim sum!

    In this context, 一定要 (jat1 ding6 jiu3) acts as a strong recommendation or insistence.

Common Mistakes

  • Using 一定要 for logical deductions.

    佢一定要喺房。
    佢一定係喺房。

    In Cantonese, '佢一定要喺房' means 'He is required/forced to be in the room.' If you mean 'He must be in the room (I assume so),' you must use 一定係.

  • Using 一定唔係 when you mean 'not necessarily'.

    Different Meaning佢一定唔係老師。
    佢唔一定係老師。

    佢一定唔係老師 is natural: 'He is definitely not a teacher.' For 'He is not necessarily a teacher', put 唔 before 一定: 唔一定係.

How It Connects

Tap a pattern to see what it builds on and what it leads to.

一定要/一定係Level 3Must Do vs. Must Be

Learn This First

To understand 'must do' vs 'must be', you first need to understand the basic copula '係' (to be) and the modal verb '要' (to need/must). Combining these with the adverb '一定' (certainly) creates the distinction between an obligation to act and a logical conclusion about a state.

Words in This Pattern