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If "can" and "be able to" are interchangable sometimes, for example:
She can speak Latin = She is able to speak Latin
Can "be able to" be used instead of "can" in:
She can't have drunk that much coffee = She isn't able to have drunk that much coffee
It can be possible that he has forgotten about us = It is able to be possible that he has forgotten about us ?
Michael Azarenko
Posted 2020-06-05T13:03:52.380
Reputation: 989
3
The short answer is no. The exchanges don't work.
In some contexts you might turn She can't have drunk that much coffee (which is fine) into She isn't/wasn't able to have drunk that much coffee but it's an uncomfortable mouthful.
She wasn't able to.... is far more likely to be used in a context such as She wasn't able to reach the the fruit without using a ladder, referring to someone's physical limitations.
It can be possible that he has forgotten... is not idiomatic. People would simply say It is possible that he has forgotten....
Is able to be possible.... doesn't work at all. We don't generally use able after it. Creatures are able, organisations and governments are able. We even talk about machines and vehicles being able. But it isn't able unless we already know what it refers to. That's to say that you can't use a placeholder it, as in It is able to rain when you mean that it might rain.
Ronald Sole
Posted 2020-06-05T13:03:52.380
Reputation: 19 044
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Why is "She wasn't able to have drunk that much coffee" okay but "She isn't able to have drunk that much coffee" bad? The difference is in the Tense only. Let's change "possible" for 'true". 'It can be true that he has forgotten" - okay or bad? So, if we talk about a homeless cat, we can't say "It is able to jump high:. If this cat is mine and I love him, speaking of him using "he", I can say "He is able to jump high", but the subject doesn't change - it's still the cat. Sometimes you say "it", sometimes "he".
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1@MichaelAzarenko No, "she isn't able= present, to have drunk=past: She wasn't able to have drunk. But we actually say: She couldn't have drunk. – Lambie – 2020-06-05T22:14:24.590
Why is "She can't have drunk" okay if "can" - present too? – Michael Azarenko – 2020-06-06T01:51:19.470
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Your first substitution, "She isn't able to have drunk that much coffee." isn't possible because of the tense of "isn't". With "wasn't", it is possible but unlikely.
For your second example, the original sentence, "It can be possible that..." is unlikely itself, because "can" and "be possible" are redundant:
"It could be that he has forgotten" already means "It is possible that he has forgotten..."
("Could" is past tense form of "can".)
That makes the substitution "It is able to be possible that...", basically impossible.
Jack O'Flaherty
Posted 2020-06-05T13:03:52.380
Reputation: 16 815
So, "She isn't able to have drunk that much coffee." is impossible but "She wasn't able to have drunk that much coffee." is possible but unlikely? What's changed? Only the tense, nothing else. How does it work?
Okay, let's change it a little. "It can be true that he has forgotten..." = "It is able to be true that he has forgotten" – Michael Azarenko – 2020-06-05T14:29:24.243
1First question, yes. Still unlikely, even with "wasn't". The rest of the sentence is speaking about the past, so you can't use the present tense "isn't". Second question, at Google books I find multiple instances of "it is able to be". The ones where "it" has a concrete antecedent seem like reasonable uses; the ones where it is a dummy pronoun, as in your example, seem very unidiomatic. – Jack O'Flaherty – 2020-06-05T14:47:50.287
If I can't use "isn't" because the rest part is speaking about the past, how can I use "can't" if it's present, too? Concrete antecedent? – Michael Azarenko – 2020-06-05T14:57:20.373
1No, you're mixing up two different answers. As to the tense, "couldn't have drunk" is probably the correct tense, but "can't have drunk" doesn't seem as impossible as "isn't able to have drunk". I'm not sure why. Maybe a new focused question would elicit a better answer. – Jack O'Flaherty – 2020-06-05T15:21:32.370
2This isn't right. The utterance She isn't able to have drunk that much coffee might not be particularly *likely*, but it's syntactically fine, and quite capable of being meaningfully interpreted. – FumbleFingers Reinstate Monica – 2020-06-06T15:36:02.357
1@FFRM, I disagree, not on syntactic but on semantic grounds. You'd be saying she is not able, at the present time, to have drunk that much in the past. – Jack O'Flaherty – 2020-06-06T15:41:43.017
@FumbleFingersReinstateMonica, so it's a correct sentence? – Michael Azarenko – 2020-06-06T16:22:46.817
2@Michael: For your purposes it's probably safer to just say it's *not* a "correct sentence". I'm simply arguing with Jack as regards whether it might be syntactically invalid and/or incapable of being parsed by a native speaker. But there's really no chance you would ever be likely to use such an utterance "correctly" even if both of us were to agree that it's at least "credible". – FumbleFingers Reinstate Monica – 2020-06-06T16:32:56.070
But what's the problem? "can't have drunk" is okay but "isn't able to have drunk" is most likely not. "Can" and "be able to" can mean the same thing. They should be interchangeable here. All of this is very deplorable...:( – Michael Azarenko – 2020-06-06T16:38:20.337
1@FFRM Just to clarify what I mean, I think "She can't have drunk that much." could be replaced by "It is not possible that she drank that much.", but not by "She is not able to have drunk that much."; so I think "can" can't always be replaced by "is able to", again on semantic grounds. – Jack O'Flaherty – 2020-06-06T16:43:52.243
1@MichaelAzarenko Don't be sad! :-) – Jack O'Flaherty – 2020-06-06T16:44:44.857
Hm, what about "could"? I heard it was totally okay to say "She wasn't able to have drunk" instead of "She couldn't have drunk". Seems to be "can't" can't here be replaced by "is not able" but "couldn't" can be replaced by "wasn't able". What a paradox... – Michael Azarenko – 2020-06-06T16:50:42.380
@JackO'Flaherty "*She is not able to have drunk that much"* is grammatical. So is *she was not able to have drunk that much.* It's exactly the same as the optional backshifting in reported speech. Both of these are acceptable: (1) *She said the earth was round.* (2) *She said the earth is round.* The only difference is the emphasis. You might not *like* one of the forms, but that doesn't preclude its use by other people in a way that they understand.
@JasonBassford On this one, at least for the example "She is not able...", I'll continue to disagree. – Jack O'Flaherty – 2020-06-06T19:55:30.117
1"It is able to be possible" is not grammatical in English. You mean: It could be possible. – Lambie – 2020-06-05T15:30:25.150
I was told "It can be posible" was bad. How can "It could be possible" be okay? – Michael Azarenko – 2020-06-05T15:35:08.567
1There is no need to say: It can be possible. If it can be possible, it is possible. However, it would be possible is idiomatic, if you believed me. For the past tense re the coffee and can: She could have drunk that much coffee. could is the past of can. – Lambie – 2020-06-05T16:28:26.630
What if I am unsure whether it's possible? "It can be possible, I don't know" – Michael Azarenko – 2020-06-05T17:27:11.540
1No, it might be possible, I don't know. – Lambie – 2020-06-05T17:41:55.870
Why not "It may be possible, I don't know? – Michael Azarenko – 2020-06-05T17:52:16.393
1It may or might,but not can. – Lambie – 2020-06-05T18:10:41.030