How could you do/have done it?

[Marika33]

I'm trying to figure out which, the simple or the perfect infinitive, you should use after "could" in these two cases.

1. [Somebody did/has done something extraordinary.] You ask that person:

• How could you do it?
• How could you have done it?
  

2. [There was a fight between two men. One lost.] The one that lost asks himself:

• How could I lose?
• How could I have lost?

 

[emsr2d2]

In the first, "How could you do that?" is more natural than "it".
In the second, of the two, I'd probably use "lose" but " have lost" isn't wrong. I'd actually say "How [the hell] did I lose?"

 

[jutfrank]

1. [Somebody did/has done something extraordinary.]

How were you able to do that?
How did you manage to do that?

2. [There was a fight between two men. One lost.] The one that lost asks himself:

How did I lose?
How could I lose?

 

[Marika33]

1. [Somebody did/has done something extraordinary.] You ask that person:

How were you able to do that?
How did you manage to do that?

That's exactly what I thought! But (unfortunately, I don't have the source) I've heard this line said by a native English speaker.

• [Somebody's just done something cool]
  His friend: How could you do that!?

2. [There was a fight between two men. One lost.] The one that lost asks himself:

As for this situation, I've heard a native speaker say, "How could I have ...", and I assumed that he wanted to say, "How could I have lost?", but stopped for some reason.

To say I'm confused is to say nothing.

 

[jutfrank]

That's exactly what I thought! But (unfortunately, I don't have the source) I've heard this line said by a native English speaker.

You needn't take everything every native speaker says as a perfect model of good English.

• [Somebody's just done something cool]
  His friend: How could you do that!?

As for this situation, I've heard a native speaker say, "How could I have ...", and I assumed that he wanted to say, "How could I have lost?", but stopped for some reason.

Yes, that's probably right.

To say I'm confused is to say nothing.

Where's the confusion? We're suggesting to you what we think is the best way of expressing yourself.