Could have p.p.

[angryinch]

In the Harry Potter, there is this sentence.

As the snake slid swiftly past him, Harry could have sworn a low, hissing voice said, "Brazil, here I come. Thanks, amigo."

And I wonder why it is 'could have sworn,' not just 'could swore.' Could it be just 'could swear' in the sentence?

[SoothingDave]

No. Your grammatical choices are "swore," "could swear" or "could have sworn." There are differences in meaning.

[emsr2d2]

In the Harry Potter, there is this sentence.

As the snake slid swiftly past him, Harry could have sworn a low, hissing voice said, "Brazil, here I come. Thanks, amigo."

And I wonder why it is 'could have sworn,' not just 'could swore.' Could it be just 'could swore' in the sentence?

"Could have sworn" has a very specific meaning. It's based around the fact that in legal terms, you swear to tell the truth in court. It's used in two main ways:

1) When something happens that you can't actually prove but you are quite certain actually happened (as in the Harry Potter quote). It's entirely possible that there was no voice saying "Brazil, here I come..." but if asked in a court of law, Harry would have been quite happy to "swear" that he definitely heard the voice.

2) When you find out that something you thought was right is actually wrong, and you express surprise.

- My car is red.
- Is it? I thought you had a blue car.
- No. It's definitely red.
- Wow. I could have sworn it was blue!

Again, you are saying that you were so certain that the car was blue that you would have been prepared to swear that that was the case in court if necessary.