Can somebody explain when to use could have and could have been and under what circumstances? Please explain with an example.
Is it something to do with the active (could have) and the passive voice (could have been)?
I think, if I have understood correctly, that this rule also applies to (would have/ would have been) and (should have / should have been).
We can use 'could have' to talk about something somebody was capable of doing in PAST but didn't do. (Possible in Past)
I could have gone to Oxford University but I preferred Harvard.
She could have married him but she didn't want to.
They could have bought a house here 20 years ago but chose not to.
We can use 'could have been' to talk about possible present situations that have not happened. (Possible in Present)
I could have been earning a lot as an accountant but the work was just too boring.
He could have been Prime Minister now but he got involved in a big financial scandal.
They could have been the market leaders now if they had taken his advice.
The former goes with any word. "I could have gone with him" or "I would have gone with her." The latter is just adding a verb to the former, the past tense of to be, which is a linking verb. "I could have been a student" or "I would have been at this place."
TL;DR: The former is just the auxiliaries. The latter is one of the things you can put behind the auxiliaries. You cannot have "could have" alone unless you are using "have" as a main verb and not an auxiliary.
Is it something to do with the active (could have) and the passive voice (could have been)?
It is not an active or passive voice issue. They are both active here. Could is a modal verb, expressing possibility. (would and should, as you write later, are also modal verbs, signifying potential and obligation moods, or voices).
Theirs is a difference of tense. Could is the preterite (past, basically) form of can (also, would and should are the preterites of will and shall).
Examples of could have in simple use:
I could have stayed, but it was late and I had to work the next day.
I could have gone (shopping), but I was waiting for the repairman.
I could have 7 tickets in this hat. (This is a special example)
Note the bolded constructions are have + past participle : the present perfect tense. As that links states, "The present perfect is used to indicate a link between the present and the past. The time of the action is before now but not specified...". Note that although the time may be unspecified, it is a definite event.
So returning to these examples, we have a mood of 'possibility' and a tense of 'some time in the past.'
I could have stayed, but it was late and I had to work the next day.
At some point in the past (last night, perhaps), I had the potential to remain at some location (to stay).
I could have gone (shopping), but I was waiting for the repairman.
At some point in the past (maybe yesterday), I had the potential to go shopping.
I could have 7 tickets in this hat. (This is a special example)
This is a special example as I stated: the verb to have here simply means to have, as in to possess, hold, or keep. The tense in this sentence is actually past only because it is not referring to a real event (see conditional / irrealis mood). So it's not even that it is past, but that it exists outside of tense.
OK! So what about could have been? The passive voice is used when the subject is not known or not used for some other reason. You may be mistakenly associated this construction with had been, which is passive (e.g., The door had been shut). Note that could had been is grammatically incorrect.
The have been construction is used with the present perfect continuous tense, denoting a time period (not an event) that occurred before now.
I could have been at home watching TV, but I had to stay late in the office finishing the report.
Normally, I go home and watch TV for some period of time. But this reality was not a possibility since I had to finish work at the office.
I could have been shopping, but I was waiting for the repairman.
It was my plan to go shop for some period of time. Although it was a possibility, I could not realize the possibility since I was at home waiting.
xxxWRONGxxx I could have been 7 tickets in this hat. xxxWRONGxxx
Note here that this in ungrammatical, as this is not an auxiliary verb usage of have. This sentence would only work in a Bill Watterson / Douglas-Adams-esque world (e.g., I could have been 7 tickets in this hat, but my transmogrifier was broken)
There are 4 combinations of could 1. Could +base formof action verb which means possibility eg , i could go to the party if iwas not preoccupied. could -was possible to do something i could write my exams well today.
2.could be+ a descriptive word you could be honest -meansit was possible for u to be honest. Could be + verb+ing I could be working in a school by next year if i graduated this year.-future possibility
Could +have -indicates a possible past action which was not done by the subject eg: she could have gone to the party but she was not interested.
Could have been +verb ing----meaning this action would have been going on possibly eg:i could have been studying at this time if u had not come come to see me
He could have been at party but you did not notice. I could have studied till 12:00PM but i did not. They could have reached their home.
I went your home at 7:00PM but you did not see over there Rep:- I could have been at terrace.
'been' is the perfect tense of 'am/is/are'. E.g. "I could have been successful," in simple tense would be, "I can be successful." For a quick refresher of tenses, click this red text.
Use 'been' if the present simple tense of the sentence has has the form "'subject'...'is/are/am'..." E.g simple "She can be a fire fighter? She is fire fighter!" goes to perfect tense "She could have been a fire fighter? she has been a fire fighter!" All passives have 'is/are/am' in them. So yes, passive perfects will always have 'been' in them.
Don't use 'been' if the simple tense of the sentence has the form "'subject'...'verb'..." E.g simple "I smile" goes to perfect "I have smiled".
You also seem to have the right idea about 'would have, could have, should have' vs 'would have been, should have been, could have been." the same thing with just a different tense.
Here is a fun example. "Where have you been?" Note that order is funny in English when asking a question. The same sentence as a statement would be "You have been where." In simple it would be "You are where." And finally, back in the form of a question, "Where are you?"
We use 'could have' to talk about something of a past possibility that didn't happen. For example:
I could have read the book./I could have saved you.
On the other hand, we use 'could have been' to talk about a present possibility that hasn't happened yet. And we use it before an -ing verb. For example:
I could have been earning a lot but the work was too hard.
