Are they always interchangeable or subtle meaning differences occurred when we prefered one to another?

Here some sentences I came across. Can we rewrite these sentences with keeping their meanings?

General: We may have been able to save victims, we'll never know.(original sentence)

Possible variations:

General: We might have been able to save victims, we'll never know.

General: We could have been able to save victims, we'll never know.

General: We would have been able to save victims, we'll never know.

Another example sentence :

If he had worked harder, he may /might/could/would have been able to get A at the exam.

Another example sentence :

I may/might/could/would have gone to university but I decided to get a job.

  • I don't know that there's an overarching single answer to this question, but there are lots of similar questions on the ELL and ELU exchanges. Here's one that nearly fits. There are differences among the words' meanings and applications. Commented Feb 21, 2015 at 3:02
  • Thank you for your comment.I know these words is used in different meanings but I just ask in the sense of original sentences.I know they have possibility, probability,ability, permission sense.
    – Mrt
    Commented Feb 21, 2015 at 3:14
  • 1
    Specifically based on your example, might could directly replace may, could is close, but slightly different. Here it would likely be saying that they thought the probability of saving victims high, rather than unknown. Would would not work here at all. It's a statement of 100% probability, so it doesn't make sense to say that followed by "we'll never know." In the other two examples, each verb would work, but there are increasing levels of probability from might --> may --> could --> would, at least as I read them. Commented Feb 21, 2015 at 3:21
  • @JasonPatterson Thank you. if General says "We would have been able to save victims" does it sound as if they had an opportunity to save the victims and if they had done something ( with a little effort )now victims will be likely to alive.Kind of neglecting.And could somebody ask " why didnt you do then?" (if the general uses the word would) in this situation?
    – Mrt
    Commented Feb 21, 2015 at 3:33
  • Here is how I read the sentence using "would" with a bit more context. Me: "General, why weren't you able to help the villagers after the rebels attacked?" General: "We would have been able to save the victims if we had not already been engaged with a separate force 100km south." Basically, if event A had happened, then event B would have occurred with 100% probability. I wish I were able to put this into a proper answer, but I'm far less certain of may/might; it's one of those things I know how to use but don't know how to explain... Commented Feb 21, 2015 at 3:39

1 Answer 1


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."


"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."

  • + 0.9 I think We may have been able ... can only be read as present uncertainty about the outcome of a past event: "It is possible that we have been able to save the victims, but we won't know until the doctors are finished." We might have been able ... may be understood in that sense, with perhaps a little more hopefulness, but it may also be understood as a past counterfactual: "It would have been possible for us to save them if we had arrived ten minutes earlier." Commented Feb 21, 2015 at 3:51
  • well maybe I should add that in the original context the general makes another sentence like : " That saving the victims might have been possible, but he added they would never know for sure "
    – Mrt
    Commented Feb 21, 2015 at 4:02
  • @StoneyB Good point about present uncertainty without a hypothesis. I'll add that. About the different levels of hopefulness: I went back and forth on which was more hopeful, and decided it was too hazy to even talk about. I'll think about might as an equivalent for would; I'm worried about confusing the OP with too many alternatives. The main thing to know is the main thrust of each word; knowing how much it can be bent or stretched in different situations can only come from experience.
    – Ben Kovitz
    Commented Feb 21, 2015 at 4:02
  • One point I will add: in the negative, "may not" is ambiguous, and best avoided in any technical or formal writing. "The name may not start with a digit" can mean either "must not" or "might not". Sometimes the context makes it clear which is intended, but generally, replacing "may not" with "might not" or "must not" is always an improvement. Commented Oct 26, 2018 at 8:33

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