Is "couldn't have pp" always past incapability a speculation as well?

[keannu]

Can anyone answer if "could not have built" in the paragraph is a speculation or past incapability?​

"......Believers in alien visits to our planet argue that there is historical evidence to support their view. They point to the pyramids in Egypt and Mexico and the size of the Easter Island statues, saying that people in ancient times could not have built them........"​

The below is an extract from a grammar website. If "could have pp" is a speculation, there should be a negative speculation as well, but the website seems to say negative one is always an incapability, so I'm confused. If so, what is the difference between "couldn't build them" and "could not have built them"? Your kind answer will be highly appreciated.​

=======================(from a grammar website)
1.We can use 'couldn't have' to talk about something we were not capable of doing.
· I couldn't have managed without you.
* I couldn't have got the job. He was always going to appoint his nephew​

2. We can use 'could have' to speculate about what has happened. (We can also use 'may have' or 'might have' in these situations.)​

• She could have taken the earlier train.
• Simon could have told her.

 

[5jj]

Can anyone answer if "could not have built" in the paragraph is a speculation or past incapability?​

"......Believers in alien visits to our planet argue that there is historical evidence to support their view. They point to the pyramids in Egypt and Mexico and the size of the Easter Island statues, saying that people in ancient times could not have built them........"​

Hypothetical, counterfactual inability. In fact they were able to build them, thanks to the alien visits.

What is the difference between "couldn't build them" = were unable to build them (and so did not build them) and "could not have built them" = would have been unable to build them (in other circumstances, but did build them).

​

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[keannu]

I fully understand the hypothetical assumption, but I kind of doubt as when I saw the next line, I was confused.

"......Believers in alien visits to our planet argue that there is historical evidence to support their view. They point to the pyramids in Egypt and Mexico and the size of the Easter Island statues, saying that people in ancient times could not have built them. They believe that the pyramids of Mexico and the carvings within them are the work of an alien civilization. They also say that the carvings are images of astronauts in spacecraft and the pyramids are too advanced for their time........"

It seems to say people didn't build them, but they were built by aliens, so "could not have built them" seems to say a factual thing. I'm not sure. If people might have built them by the order or help of aliens, it makes sense, but if they were entirely built by aliens and there was no work of people, then it means people's inability.. So confusing!!​

 

[5jj]

"......Believers in alien visits to our planet argue that there is historical evidence to support their view. They point to the pyramids in Egypt and Mexico and the size of the Easter Island statues, saying that people in ancient times could not have built them. They believe that the pyramids of Mexico and the carvings within them are the work of an alien civilization. [...]."

It seems to say people didn't build them, but they were built by aliens, so "could not have built them" seems to say a factual thing. I'm not sure. If people might have built them by the order or help of aliens, it makes sense, but if they were entirely built by aliens and there was no work of people, then it means people's inability.. So confusing!!​

It is even more confusing if you give insufficient context!

The next line you quote makes it clear that the people did not build them.

How often do we have to say in these threads, "Context is important"? I interpreted the dots at the end of your, "They point to the pyramids in Egypt and Mexico and the size of the Easter Island statues, saying that people in ancient times could not have built them........" as suggesting something like, "without the help of the aliens". For that context, my interpretation was correct. If you change the context, you change the meaning.

Modal verbs can convey a range of meanings, and when we get into the range of hypothetical forms, the range increases. Let's just take one example, he could have gone, and two interpretations.

1. If Luke had had the money, he could have gone to America.
2. If Luke had the money, he could have gone to America.

In #1, the implication is that Luke did not have the money, and so he was not able to go. He did not go.
In #2, the implication is that it is possible that Luke had the money and, in that case it is possible that he was able to go. It is possible that he went.

If you look at just these two sentences, it seems very confusing, but you cannot look at just individual sentences, particularly with little or no context. You need to understand the possible meanings of modal verbs, and how English uses modality and tense to convey idea of modality, conditions, possibility, hypothesis and counterfactuality.

 

[keannu]

Thank you so much, and I'm really sorry for the insufficient context, I finally grasped the explanation, so it's clear,but still I have the doubt about the below.
As you said, depending on context, "could have pp" can be either contry-to-fact imagination(in conditional 2 and 3) or speculation or assumption that could be true or false (in conditional 1). I fully understand the difference.

But I encountered the below example and some lines in American dramas that don't belong to the two categories you explained. It just seems to bear almost no difference with "couldn't do something".
Is this a third category in the world of "could have" confusion?

=======================(from a grammar website)
1.We can use 'couldn't have' to talk about something we were not capable of doing.
· I couldn't have managed without you.
· I couldn't have got the job. He was always going to appoint his nephew.
· I couldn't have enjoyed myself more. Thank you for a lovely day.
​

 

[5jj]

=======================(from a grammar website)
1.We can use 'couldn't have' to talk about something we were not capable of doing.
a· I couldn't have managed without you.
b· I couldn't have got the job. He was always going to appoint his nephew.
c· I couldn't have enjoyed myself more. Thank you for a lovely day.

These fall into the same category as what you called 'past incapability' in your first post, as does 'people in ancient times could not have built them'.