조동사

• 10 조동사

  10.1

  can 与 could (能力、请求)

  

  English

  

  can expresses ability or possibility; could is the past tense of can, and is also used for more polite requests. All modal verbs are followed by the base form of the verb.

  我I 会can 游泳swim.

  I can swim.

  她She 会could 读read 在at 四岁four.

  She could read at the age of four. (Past ability)

  能Could 你you 帮help 我me 请, please?

  Could you please help me? (Polite request)

  Note

  • After a modal verb, use the base form: ~~can to swim~~ ✗ → can swim ✓.
  • Negative: cannot / can't, could not / couldn't.

  10.2

  should (建议)

  English

  should expresses advice or "should".

  你You 应该should 看see 一位a 医生doctor.

  You should see a doctor.

  我们We 不应该shouldn't 浪费waste 水water.

  We shouldn't waste water.

  Note: should gives advice and is less forceful than must; it is also followed by the base form of the verb.

  10.3

  must 与 have to (义务)

  English

  Both express "must":

  • must: Often indicates something the speaker considers important, or a rule.
  • have to: Often indicates an external requirement (regulation, objective necessity).

  你You 必须must 系wear （冠词）a 安全带seatbelt.

  You must wear a seatbelt.

  我I 不得不have to 起床get up 早early.

  I have to get up early.

  Note

  • mustn't = "prohibited": You mustn't smoke here. (Smoking is prohibited here.)
  • don't have to = "not necessary": You don't have to come. (You don't need to come.)
  • Note that their meanings are completely different: one means "forbidden," the other means "not necessary."

  Common Errors

  • ❌ ~~You must to wear a helmet.~~ → ✓ You must wear a helmet — All modal verbs (can / could / should / must) are followed directly by the base form and never take to.
  • ❌ ~~She musts study harder.~~ → ✓ She must study harder — Modal verbs do not take a third-person singular -s.
  • ❌ Wanting to say "you don't need to come" but saying ~~You mustn't come.~~ → ✓ You don't have to come — mustn't means "forbidden," while don't have to means "not necessary." Their meanings are exactly opposite.
  • ❌ ~~Yesterday I must work late.~~ → ✓ Yesterday I had to work late — must has no past tense; use had to for past obligations.

모든 주제 · 영어 문법 · A2