In the first example the writer is describing a general situation. They do not expect this to happen generally for any disease or any drug although it might in a specific case.
In the second case the writer is describing a specific situation. We know that for this disease no drug works for everybody and if it does work for someone it will not work for that ...
The second one is appropriate, because assuming from the context, the "changes" haven't been made yet. So if they are made, they will be made in the future, so 'will' is appropriate. We hardly ever use 'would' instead of 'will' when the future of both 'now' and the past is the same.
He might have gone = There was a possibility that he had already gone. (past tense)
He might go (and I might go) refer to a possibility either in the past or the present. We thought he might go, but he didn't. I might go out later if it stops raining. He might go doesn't really fit with '...but luckily we reached his house and found him'.
From my answer to a similar question
Can = have the ability to
Could = have the potential of
No one can fool me. (no one has the ability to fool me)
No one could fool me. (no one has the potential of fooling me)
How could we spend this time on the island?
By what means (hotel, money. a tent etc.)
What to do while there, the activities, in the sense of how to spend one's time.
There is also a use of could that goes to surprise about a person's actions.
How could you do this to me? [It expresses outrage or anger]
How could we spend this time on the island [when ...
As you say, the first is hypothetical (grammarians say irrealis or counter-factual).
Without my coach it wouldn't be possible => If I didn't have my coach it wouldn't be possible, but I do have it.
The second is an unknown possibility, but is not counter-factual, or irrealis:
Without my coach it won't (will not) be possible => If I don't have my ...
Could (have the potential)
Can (have the ability)
Couldn’t fill a concert hall (lack potential of filling a concert hall)
Can't fill a concert hall (lack ability to fill a concert hall)
If 'couldn’t' is the past tense of 'can', then it means the same as #2
What will you do if... implies that you think something is quite likely to happen ('if it rains').
What would you do if..., as you say, is more likely to be used with a hypothetical situation.
Of course you can ask someone what they 'will do' if something unlikely happens, but it would sound strange.
Can refers to ability. If you can do something, you're able to do it--it doesn't mean you will do it, or have to do it, but you are able to do it.
Must means not having a choice to do something. If you must do X, you don't have a choice not do X.
Keep in mind modals in English are often "misused" for politeness and authority-deference purposes. ...
The first examples are what is called the epistemic use of the modals "can" and "must": they're saying things about the speaker's knowledge and expectations, not about possibilities or powers in the real world. They both say "I am sure that" or "I conclude that" it isn't broken. Certainly can't is more likely there in ...
You are asking for more examples for the usage of the word "would."
The word "would" is also used as the past tense of the word "will." For example:
I will say that is true based on what I know. [All the verbs are present tense: will say, is, know.]
I would say that is true if I knew for sure what time the other ...
"I did not have to meet him there" could mean "I was not required to meet him there", or it could mean "I could have met him somewhere else", but "I need not have met him there" only means the second of these.
There is no difference in meaning, only in use. If you are in a formal location, it is more recommended that you use did not have to. If you are in a place that does not require you to be formal, you can choose which one you prefer to use. I think the first one sounds like something more complete, but that's just a personal opinion.
I have [to go there].
I must [go there].
In these examples, the bracketed elements are subordinate infinitival clauses functioning as catenative complement of "have" and "must".
The sentences as a whole are called the matrix clauses, within which the infinitival clauses are subordinate.
Thus, you could if you wished call "have" ...
I like to go there.
I want to go there.
I need to go there.
I have to go there.
Under a traditional analysis, "like", "want", "need" and "have" are all main verbs in these examples. The verb "to go" is a full infinitive. The infinitive phrase "to go there" is the direct object of the main verb. ...
It's a good question. A dictionary will tell you that "have to" is an order that implies some obligation to obey, but often when it is used the speaker has no actual authority over the person they are saying it to - it is just to make the statement more emphatic.
You should stop eating that much.
"Should" implies that there would be ...
1) The best match in Merriam-Webster's listing is definition 4 — used in [an] auxiliary function to express probability or presumption in past or present time. Here, it seems to be a presumption about a hypothetical past. He hadn't been baffled, but he would have been.
2) Only the first verb in a predicating phrase has tense and attaches to a subject. ...
So here, the “he” in question is not “baffled by the way the crime was committed,” but he “would” be (“undoubtedly”). I strongly suspect that “he” is not “baffled” primarily because “he” doesn’t know about the crime or how it was committed in the first place. If he later learns about it, for example, then the speaker expects him to be baffled by it.
This is ...
From your post:
The speaker addressing this is the subject's—Barry—spouse.
I take it that means that Barry's wife is saying that line.
Yes the two verb forms are natural, if it means this:
"Barry wouldn't give up and the woman he married (I) won't either.",
where "wouldn't" refers to the past, and "won't" refers to the present ...
A would have won.
Would have is the part of the third conditional, but it can be used without an 'if clause'. It means it was possible for A to win, but A didn't win.
A should have won.
It means winning of A was a good idea, but A didn't win anyway.
Can I use the following sentence to talk about my future inability?
Is the second sentence talking about my inability to dream of a better vacation only in the past or is it talking about my inability to dream at any time?
in the past
There was a time when X could never have kept me spellbound. (Hypothetical - X didn't try to keep me ...
If it is followed by a video of locusts devastating India's food grain reserves, "can" would be more appropriate than "could". If the video related to a different country "could" would be better than "can". In this context "can" and "could" both refer to possibilities for the future, but "can" is more immediate, and needs stronger evidence.
I think A and C refers to a permanent future situation or in what condition things will be in the future.
As for B and D, The present tense suggests these conditions were true in the past, are true now, and will continue to be true for a foreseeable future.
If you're speaking about what is generally true, your alternatives a and b mean the same thing.
But in the examples c and d of the jar, you are talking about a particular jar, which may or may not have anything in it.
"This jar holds a kilo." may be a statement about its contents right now, or about its capacity.
"This jar will hold a kilo." is a ...
Oddly enough, "I couldn't" is polite middle-class British English which effectively means:
"Yes please, but I don't want to sound greedy so I'm going to pretend to refuse it and expect you to generously (and of course politely) insist, after a few rounds of which I am then going to graciously accept with all the language of deferential reluctance."
On such ...
For me, 'could' is a more logical future tense of 'can', because 'will be able to' is the future tense of 'can' when we talk about ability. So when we talk about possibility, we have to use 'could' to express 'can' in the future.
I think the main source of confusion is your idea of a "full version" of each phrase. As is mentioned in the comments, the second phrase isn't a "full version" of the first phrase. In fact, it's no more "full" than the first phrase.
Now, let's start at the beginning of your post. You claimed not to have understood the following:
She hoped to have done...
"She hoped to do it."
It means she hoped to do it & she did it.
"She hoped to have done it."
Here, the perfect infinitive signifies that she hoped to do it, but she didn't do it.
"She can't have done it"
= It is not possible that she has done it. (Or, I don't believe that she has done it.)
"She couldn't have done it"
= It was not ...
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 ...
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 ...
The first thing I do in the morning is check my mobile phone
This is perfectly grammatical and perhaps the most common. When the subject has a form of "do", the infinitive is used. You can put "to" there, but it is optional.
The first thing I do in the morning is checking my mobile phone
The sentence above is not grammatical. It'll only be grammatical ...
Saying you 'can' see something might imply that you aren't looking at the thing at the moment of speaking. "I can see the oak tree from my window." doesn't necessarily imply that you're looking out the window at the tree at that moment, or even that you're in the room or the house with the window referred to.
But it's also used in cases where someone could ...