What is the meaning of "would", and how to use it?
All modals have several meanings. Most common are
the Epistemic sense of a modal, which refers to logical conclusions
This must be the place, This can't be the place, This would be the place.The Deontic sense of a modal, which refers to sociocultural obligations and affordances
You must be careful, You can't do that, He wouldn't dare.
The first three uses of would are, as @Cathy points out, equivalent to epistemic must.
I.e, like all epistemic modals, they state a conclusion made by the speaker from
some kind of evidence or presupposition, rather than an assertion of fact.
It seems likely that (1-2), for instance, are short for something like
- (if I were to guess, I would say that) that would be John/Ram.
(3) is almost the same -- (If I were to guess, I would say that) they were ...
(4) and (5) are different. For one thing, they're stressed main verbs, not auxiliaries.
For another, they're deontic, not epistemic. Deontic would has to do with being willing
(will (n) and will (v) and willing and willful and would are all from the same root).
So, to say that somebody would do something (with a stressed would, and especially with a deleted main verb, as in 4) is to say that they are willing (and therefore likely) to do it under certain conditions.
Note that in (5) there are two modals -- deontic would and deontic have to, so what's being said is that he was willing, and indeed obliged, to say that under certain conditions.
And these are not the only possible senses of would, either.
That would be Ram calling. I'll answer it.
The guy on the phone had southern accent. That would be Tom.
“We saw a police helicopter overhead yesterday morning.”
“Really? They would have been looking for those bank robbers.”
1., 2. and 3. would = must
In 1., 2. and 3., would and must are interchangeable:
1. That would/must be John calling.
2. That would/must be Billy.
3. They would/must have been looking for those bank robbers.
- You would have to say/do that.
Trust you to say that. / I'm not surprised you said that. / It's something you would typically say.
Here, would and must aren't interchangeable.
You can't say: "Well he must, mustn't he?" - It's wrong.
- John said he didn't steal any money. Well, he would, wouldn't he ?
The meaning of: "Well he would, wouldn't he?" is that it would be typical of John to deny stealing the money, so the conclusion is : "He must have stolen the money."
- In sentence one, That would be John calling. I'll answer it, the word would is used as a way of expressing your opinion. It can also be understood as a way of expressing an informed decision based on information you might know. For example, you were expecting John to call you at that time. Since you got a call at the specified time, it's reasonable to assume that it was probably John calling.
- In sentence two, The guy on the phone had a southern accent. That would be Ram, the word would is again used in the same way as in sentence one. You're making an informed decision or conjecture. What the sentence means is that, the person talking on the phone is most likely Ram. He might not be Ram. But YOU think it is highly likely.
- Again, in sentence three, We saw a police helicopter overhead yesterday. They would have been looking for those bank robbers, the word would is again used to make a conjecture. You are using it to make a statement regarding something that is highly likely.
- In sentence four, John said he didn't steal money. Well, he would, wouldn't he? , you use the word would in conjunction with the word wouldn't to make a statement to mean that it was obvious that John wouldn't admit to his theft. Since, in most cases, thievery is frowned upon, no one would own up to thieving. So, when you use would here, it can be understood to mean that the logical course for John to follow is to NOT own up to his illegal action and thus, John doesn't plead guilty, saying that he hadn't committed the theft.
- In sentence five, You would have to say that, the word would is used to signify that you were REQUIRED to say that. Or rather, that the best course of action was to say that. Another way to look at it is that you had no other choice but to say that.