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Hi,

How can you eat that stuff? Gross! (How can you = How is it possible that you do...)

I'd like to know how to make that negative, with a meaning "How is it possible that you don't..." - Should I say "How can't you...?", like "How can't you know that? Everybody knows!"

How could you do that to your mother? (How could you = I'm kind of shocked, I can't believe you did something like that, but you did)

I'd like to know if I can also use "How could" when I'm referring to something that didn't actually happened. Example:
How could I steal the money? I was nearly a thousand miles away from here!
Or do I have to say "How can I have stolen the money? I was..."

Thanks Emotion: smile
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How can you eat that stuff? Gross! (How can you = How is it possible that you do...)

I'd like to know how to make that negative, with a meaning "How is it possible that you don't..." - Should I say "How can't you...?", like "How can't you know that? Everybody knows!"

How can you not know that?
How can you not feel sorry for people like that?
How can you not see that the puppy needs water?


Substitute could for can in all of the above, if you wish.


How could you do that to your mother? (How could you = I'm kind of shocked, I can't believe you did something like that, but you did) Not exactly. This could be anticipatory -- a reaction to a planned action. To be unambiguously in the past (i.e., you did do it), you need How could you have done that to your mother?

I'd like to know if I can also use "How could" when I'm referring to something that didn't actually happened. Example:
How could I steal the money? I was nearly a thousand miles away from here!
You need this:
How could I have stolen the money? I was ...
Or do I have to say "How can I have stolen the money? I was..."
It's possible but, in general, no. We shy away from the can have combination, preferring could have instead, as shown above.

Slightly off-topic: The aversion for can have is most intense in the assertive form (no interrogative nor negative elements present):

I can have forgotten it.

In this case, use may or might or could:

I [may / might / could] have forgotten it. Emotion: smile

CJ
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Thank you Jim,
I'm afraid I've been interpreting "How could" the wrong way. I'd like to ask something more, with some examples in different contexts.

Criticizing:
What? You are stealing money from your mother? How could you! (also "can", right?)
What? You are stealing money from her? How could you steal money from your mother! (also "can", right"?)
What? You used to steal money from your mother when you were young? How could you! (I think this "could" doesn't refer to the past, it's just an idiom, it means "How would this be possible? I can't believe it")
What? You used to steal money when you were young? How could you steal money from your mother! (Same as above, it is not the past of "can", it's just an idiom. To refer to the past, we should say "How could you have stolen money from your mother!", but I think it wouldn't be idiomatic, it's not what we should say in order to criticize).

Not believing what we are told:
What? You are able to lift 200 pounds? How could you do that! You are not so muscular, come on! (this is in the present, "can" should be ok too)
What? In 1966, Mike Loser lifted 350 pounds? Haha, come on, how could he do that! He was always a loser... (this is in the past, and I'm not sure I can use that "could" as the past of "can", since a sentence in the present like "How can you lift that" would be ok. Or should I use "How could he have done that"?)
I didn't steal the money. How could I steel the money if I was 1000 miles away from here? It was impossible... (Same comments... How can I steal the money now? ---> How could I steal the money that day? Do I have to say "How could I have stolen..."?)

Asking with surprise:
Wow, how could you improve the graphical interface this way? How cool! -- Well, I installed some additional software... (Maybe this is really wrong, and should be "How did you manage to improve...", but since it's "asking with surprise", I'm a little confused...)

Thank you in advance,
sorry if there are too many examples, but I believe I need context to understand this, it wouldn't make sense without a specific context... Emotion: smile
Criticizing:
What? You are stealing money from your mother? How could you! (also "can", right? Right.)
What? You are stealing money from her? How could you steal money from your mother! (also "can", right"? Right.)
What? You used to steal money from your mother when you were young? How could you! (I think this "could" doesn't refer to the past, it's just an idiom, it means "How would this be possible? I can't believe it" This is a reasonable explanation.)
What? You used to steal money when you were young? How could you steal money from your mother! (Same as above, it is not the past of "can", it's just an idiom. To refer to the past, we should say "How could you have stolen money from your mother!", but I think it wouldn't be idiomatic, it's not what we should say in order to criticize I think it's still idiomatic. It is still critical either way. It is not just a request for information as in How could the ancients have built the pyramids with so little technology compared to ours?).

Not believing what we are told:
What? You are able to lift 200 pounds? How could you do that! You are not so muscular, come on! (this is in the present, "can" should be ok too Yes, that's right.)
What? In 1966, Mike Loser lifted 350 pounds? Haha, come on, how could he do that! He was always a loser... (this is in the past, and I'm not sure I can use that "could" as the past of "can", since a sentence in the present like "How can you lift that" would be ok. Or should I use "How could he have done that"? Either could or could have. I prefer could have. It's a matter of style.)
I didn't steal the money. How could I steel the money if I was 1000 miles away from here? It was impossible... (Same comments... How can I steal the money now? ---> How could I steal the money that day? Do I have to say "How could I have stolen..."? Exactly as in the previous example.)

Asking with surprise:
Wow, how could you improve the graphical interface this way? How cool! -- Well, I installed some additional software... (Maybe this is really wrong, and should be "How did you manage to improve...", but since it's "asking with surprise", I'm a little confused... I see. How could/can you improve ...? is asking for a suggestion the way I hear it. I am not familiar with the category "asking with surprise" that you seem to be focusing on here.)

CJ
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Thank You CJ

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