# Might have, may have, could have, must have, would have [closed]

Yesterday there was a driving test of my friend. But I have not contacted him since yesterday. Now I am predicting about the result of his driving test.

He might have passed the driving test (30% sure)

He may have passed the driving test (40% sure)

He could have passed the driving test (50% sure)

He must have passed the driving test (90% sure)

He would have passed the driving test (100% sure)

• I'd put "must have" at 100%, and "would have" at "well, he would have if he showed up, so it's really 100% if he showed up, indeterminate if he didn't", but that's just my take. The others seem reasonable. Mar 30, 2015 at 7:04
• OP: Read some of these threads first goo.gl/aFLCNd, then we talk:-) Mar 30, 2015 at 7:35
• Amir, minimal edits to bump a question are frowned upon and certainly won't help to get it re-opened. Apr 22, 2015 at 10:43

There is no percentage to be allotted to each sentence. To attempt to assign percentages to those sentences would be to completely ignore their grammatical meanings and implications.

If you really wish to have a mathematical perspective then read my response here: Use of subjunctive form

The subjunctive mood is the grammatical equivalent of the mathematical imaginary domain.

To assign percentages to denote the possibility of an imaginary number occurring in the real domain would be ridiculous.

As I had written, opposed to grammarians' discrete perspectives and pigeon-holing, the grammatical imaginary domain is actually a continuum of modes.

Most subjunctive sentences/phrases (like any number) is a combination of both real and imaginary domains.

• He might have passed the driving test.
Imaginary possibility towards the outcome an actual event.
Imaginary expectation due to outcome of imaginary possibility.

• He may have passed the driving test.
Unknown outcome of an actual event.
Imaginary expectation due to unknown outcome.

• He could have passed the driving test. Known and actual failure of an actual event.
Imaginary expectation of the imaginary success of an actual event.

• He must have passed the driving test.
Imaginary positive outcome of an actual event.
Unknown expectation based on the imaginary positive outcome.

• He would have passed the driving test.
Known and actual failure of an actual event.
Imaginary possibility of influence that would have resulted in an imaginary success. Imaginary success based on the imaginary possibility of the influence.

I don't have the actual time to verify the accuracy of the process flows I assigned above, so I might return to correct it.

But, the point is, this is the way to assign mathematical meaning to phrases made in a combination of real and imaginary domains.

Grammatically, all of these sentences are acceptable. But your percentages of possibility aren't really on target.

He passed the driving test.

You're 100% sure he passed.

He might/may have passed the driving test.

You're unsure how he did but it's possible he passed. The percentage of possibility isn't straightforward. It's affected by context (and even, if the sentence is spoken rather than written, inflection).

He must have passed the driving test.

This doesn't express possibility at all; it's the conclusion of a logical deduction.

He would have passed the driving test.

This also doesn't express possibility. In fact, the sentence implies that he failed the test. *He would have passed it, but something got in the way.*

He could have passed the driving test.

Depending on context, this version can work either like might/may, or like would, e.g.:

"He sounded excited on the phone. He could have passed the driving test." ...or... "He could have passed the driving test. He is an excellent driver. But his bus broke down on the way and he missed his appointment."