Why is John late?
He could have got stuck in traffic.
He must have been stuck.
He may have been stuck.
He might have been stuck.
Are there any differences (even subtle) between these answers ?
Learn English – could have – must have – may have – might have
modal-verbs
Related Solutions
Lost opportunities
The meanings of these are indistinguishable, except for a subtlety that I'll explain later:
We may have been able to save the victims.
We might have been able to save the victims.
The words "would" and "could" suggest both the past tense and the consequence of some imagined hypothesis, with either or both meanings being activated when suitable to the context. To use "would" here, you need to establish an imagined hypothesis. Then "would" indicates the consequence:
If only we had the antidote yesterday! We would have been able to save the victims.
It's possible to say "could have been able to", but "could" is the past tense of "can", so it already indicates ability. So, "could have been able to save the victims" is awkward. However, you could say:
If only we had the antidote yesterday! We could have saved the victims.
"Would have" and "could have" imply that the opportunity is now lost.
"May have", "might have", and "could have" don't require context to set up an imaginary hypothesis, but they do suggest that you have such a hypothesis in mind:
"We might have been able to save the victims."
"How?"
"The most recent antidote has been sitting in the refrigerator since yesterday."
"What? And no one tested it?"
An important difference
A very big difference between the may/might and would/could sentences is that the would/could sentences claim a high level of certainty about the hypothetical situation: the antidote is assumed to work. The may/might sentences lack that certainty. They suggest only that in the hypothetical situation (which might not even be stated yet), the antidote might have worked. "Would" corresponds to "will", and says that the antidote will work (in the imagined situation, which occurred yesterday). "Could" corresponds to "can", and suggests that the antidote can work (in the imagined situation, which occurred yesterday).
A subtle difference
"May have" mainly indicates uncertainty about what we could have done. "Might have" suggests both uncertainty and that the opportunity, if it even existed, is now lost.
This is English, so don't take that as a rule. Instead, memorize this well-known couplet (by John Greenleaf Whittier, 1856):
For of all sad words of tongue or pen,
The saddest are these: "It might have been!"
One more power of might
There's one more possibility with "might", which illustrates the flexibility of these words. "Might" can suggest that the victims actually were saved, or are actually in the process of being saved:
We might have been able to save the victims. I just read an article in a medical journal, which says that the antidote we tried yesterday was proven to work on mice in a recent experiment.
In other words, the antidote we tried yesterday might be working, right now. Since the uncertainty of the word "might" applies to our ability to save the victims, if we had that ability yesterday, then our efforts yesterday were successful, or are on the way to succeeding. Currently, we don't know (that's the uncertainty of "might"). Obviously, your listener will hear this meaning only if the victims are still alive.
You can also do this with "may have" and "could have", but those don't make the pun in the title of this section. Since "may have" has the least connotation of lost opportunity, it provides the clearest way to express optimistic uncertainty about the effects of yesterday's action: "We may have saved the victims."
It depends on whether there is an expectation that she is still busy.
I called her at six but she didn't talk to me. She might have been busy; that is why she didn't talk to me.
but you expect she might not be busy now.
I called her at six but she didn't talk to me. She might be busy; that is why she didn't talk to me.
when you expect she might still be busy.
The second would be more likely if it is now a short time after six.
Otherwise, using simple past tense is the safe choice.
Best Answer
An action he took in the past resulted in the possibility of him getting stuck in traffic in the past.
Since this possibility has passed, it ended up that he did not get stuck in traffic. Otherwise we would say "He did get stuck in traffic."
E.g. Why is Bobby late? Forgive him, he could have been stuck in the rain.
It also can be used in the same way as "might have been" below.
Something happened X, and the only reason that explains it is the fact that he had been stuck. X refers to something that is completed or completely in the past. E.g. Bobby was late because he must have been stuck in the rain. (Bobby is here now)
Something happened X, and a possible reason that explains it is the fact that he had been stuck. Other reasons for him being stuck are possible. X refers to something that may have started in the past but is happening now. E.g. Bobby is not here, he may have been stuck in the rain. (We are still hoping he makes it)
Something happened, and a possible reason that explains it is the fact that he had been stuck. Other reasons for him being stuck are possible. X refers to something that is completed or completely in the past. E.g. Bobby hasn't called. He might have been stuck in the rain. (Implication is that we don't expect him to show up)