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Can't or Mustn't

Interdiction? Incapacity? Impossibility? CAN'T?  MUSTN'T?

I) CAN 'T : - expresses incapacity, but also impossibility, ("it's impossible that..."), the interdiction to do an action (when speaking): (then it is both the negative form of CAN (a physical capacity), of MAY (permission) and of MUST (obligation).

- Yes, Kevin, as you're a good swimmer, you can go to the deep end of the pool... but no, Lucy, you can't ( here, a physical incapacity which comes to an interdiction)... You can't (a physical incapacity ) swim well enough.

- Yes, you may go out ( permission), but you can't ( impossibility which is the same as an interdiction) stay out beyond the deadline.

- You must (obligation) take your cap off, and you can't (= interdiction) put it back before you go out.

- He can't (impossibility) be responsible  for his brothers and sisters... He's much too young for that. 

I can't help= expresses the inevitable character of a fact: I have no other choice, I'm compelled...

II) Mustn't:= interdiction. ( must = obligation)

- You mustn't answer back when someone scolds you. It's rude.

III)  CAN'T HAVE + past participle: in the past, you must use the construction: "can't + have + past participle", in order to express impossibility and incapacity in the past.

- She can't have found the key... It was hidden where she couldn't go!

 
  BEWARE!  MUSTN'T isn't used in the past.

IV) Legal interdictions : no + gerund:

- "No smoking inside the building." "No walking on this lawn."

There you are! You know everything! Time to face the test ! Go for it ! Let the FORCE be with you...

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1)' No, this story is incredible... Things can't have happenedcan't happenmustn't have happenedI don't know like that !'
2) Try to do this exercise again... I'm sure you can domust docan't have doneI don't know it.
3) You must becan have beenmust have beenI don't know more careful if you want to do it properly.
4) No! You must addingmustn't addcan addmust addI don't know these two numbers... They don't belong to the same category.
5) Of course he mustn't docan docan doingcan't doI don't know the race with others if he wants to... But he can't askingmustn't askmust askingI don't know the other boys to help him.
6) Yes, you mustn't gomust gocan gocan't goI don't know to the party, but as I mustn't gocan gocan't goI don't know and fetch you there, you can stayingmust staymustn't stayI don't know after ten pm and must to walkcan walkingmust walkI don't know back home with your brother.
7) Really, Lucy, I can't helpcan helpmust helpI don't know thinking that you mustn't becan't bemust becan beingI don't know more attentive to your things: you must takecan't takingmustn't takecan takingI don't know out several games at the same time and mix them up. Just think, little girl, you can't puttingmust puttingmust putI don't know one away, back in its box, and must takecan takemustn't takingI don't know another one, then! You cannot learnmust learnmustn't learnI don't know that!