Differences between "could"/"could have" and "Would"/"would have" in the past?

Question

Hello teachers,I've been struggling with this part of grammar for long.I know that "could" in most cases is used to say that something is possible in present or future or when we want to make requests and sugestions,but I've seen many times that because "could"is  past form of "can" it can be used in the past.now we know that for the actions in the past we must use "could have" but why do we sometimes use "could" for the actions in the past as well? and what difference in meaning is between them?examples:both are used for an action in the past,but what are there meanings ? I could save him/I could have saved him.I could finish my exam in 30 mintues./I could have finished my exam in 30 mintues.I was 5 minutes late,I couldnt catch the train./I couldn't have caught the train.He couldnt go to canada because he was sick./He couldnt have gone to canada because he was sick.The situation was so bad,it could be worse./The situation was so bad,It could have been worse.Michael was a great boxer,he could beat his all opponents./Michael was a great boxer,he could have beaten his all opponents.Note:all above examples were made by me.Would/would have:I know that we  use "would" and "wouldn't" when we imagine the situation or action in the present and future when we think that they are not real.I also know that we use "would have done" when we imagine situations and actions in the past,but I've seen and heard that "would" was used for the actions and situations in the past that didnt happened.Now what are their differences when we use "would" and "would have" for the actions in the past?Examples:I knew that John would come to my party./I knew that Jhon would have come to my party.I thought you would come home early./I thought you would have come home early.I never imagined that u would betray me./I never Imagined that you would have betrayed me.Note:I know what is difference between "could" and "could have" or "Would" and "would have" in conditional sentences(IF Claues).sorry If I've asked many questions.I truly appreciate your efforts and great job you do in this website.If you answer for me,I'll be indebted to you forever.Thank you so much

CalifJim · Accepted Answer

Whew! You have an enormous number of issues here. Let me just deal with "could" for now.

I could save him. ~ I [would be able / have the ability] to save him (now). (I haven't tried.)

I could have saved him. ~ At that time in the past I had the ability to save him. (But I didn't save him. Maybe I didn't even have a chance to try to save him.)

I could finish my exam in 30 mintues. ~ I would be able to finish my exam in 30 minutes. (I haven't tried yet.)

or ~ It might be that I will finish my exam in 30 minutes.

I could have finished my exam in 30 minutes. ~ At that time in the past I had the ability to finish my exam in 30 minutes. (But I didn't finish in 30 minutes.)

I was five minutes late, so I couldn't catch the train. ~ ... so I failed to catch the train.

I couldn't have caught the train. ~ At that time in the past, there was no possibility of catching the train no matter what I might have done to try.

or ~ It is logically impossible that I caught the train at that time in the past.

He couldn't go to Canada because he was sick. ~ He was physically unable to go to Canada because ...

He couldn't have gone to Canada because he was sick. ~ He was physically unable to go to Canada because ...

or ~ It is logically impossible that he went to Canada because ...

The situation was so bad, it could be worse. Not correct.

The situation was so bad, it could have been worse. Not correct.

The situation is bad, but it could be worse. ~ ..., but worse situations [are / would be] possible.

The situation is/was bad, but it could have been worse. ~ ..., but worse situations [are / were / would be] possible.

These two are quite close in meaning. In the first, the speaker is more focused on the situation as it stands. In the second, the speaker may be more focused on the factors that brought about the situation. As for the sequence of tenses, you can't have The situation was bad, but it could be worse unless you qualify thus: The situation was bad yesterday, but it could be worse tomorrow. This makes it clear that you are really talking about two different situations.

Michael was a great boxer. He could beat all his opponents. ~ ... He was able to beat ... ~ He had the skill to beat ...

Michael was a great boxer. He could have beaten all his opponents. This one is a bit incoherent. He had the skill to beat all his opponents, but he didn't beat them all or he didn't even have a chance to try. (It doesn't seem that he was so great.)

________

could sometimes means may or might, i.e., it is possible that ... [present or future].

It [may / might / could] rain tomorrow. = It is (logically) possible that it will rain tomorrow.

- - - - - -

Note that by saying "I could" you are saying that it would be possible for you (to do something), and that this can be equivalent to offering to do it.

I could help you find a new job. (I am offering to help you find a new job.)

- - - - - -

But could not can't be used that way.

It [may / might] not rain tomorrow. = It is possible that it will not rain tomorrow.

(Not It could not rain tomorrow.)

_______

could have can therefore mean may have or might have, i.e., it is possible that ... [past].

It [may have / might have / could have] rained yesterday. = It is possible that it rained yesterday.

But could not have can't be used that way.

It [may not have / might not have] rained yesterday. = It is possible that it did not rain yesterday.

Note the meaning:

It could not have rained yesterday. = It is impossible that it rained yesterday.

_________

could sometimes means 'had the ability, knowledge, power, skill, or talent to do something'. There is also the implication of could and did (as a habit over a period of time).

When I was younger, I could [speak Italian / lift 200 pounds / stand on my head / stay up all night].

Context is important in establishing this meaning as a past ability. Without the context (underlined above), an isolated sentence like I could speak Italian, for example, might be taken as a present offer to speak Italian if the situation seemed to require speaking Italian. In this way I could speak Italian means I [can / know how to] speak Italian and I [am / would be] willing to speak Italian as required by this situation.

_____

could have has a similar meaning in this kind of context, but it's slightly more 'conditional', more 'hypothetical'. There is the implication of doing something on one occasion upon request, not necessarily habitually.

When I was younger, I could have [spoken Italian / lifted 200 pounds / ...] (if I had been asked to do so).

The negatives could not and could not have work the same way in this meaning:

When I was younger, I could not [speak Italian / stay up all night] (so, of course I did not do these things).

When I was younger, I could not have [spoken Italian / stayed up all right] (even if you had begged me to do so).

__________________

could cannot be used in the meaning 'succeeded'.

I could catch the train never means I succeeded in catching the train / I managed to catch the train.

was able to must be used instead:

I was able to catch the train means I succeeded in catching the train / I managed to catch the train.

But could not can be used in the meaning 'failed'.

I couldn't catch the train can mean I failed to catch the train.

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Try using Google and/or the search box on this site for more on this topic.

CJ

Cyrus.achaemenid · Answer

What a great and complete explanation.Thank you so much sir.

would you please correct me about "would" and "would have" that I mentioned in my first reply?

JOMB · Answer

Hi CJ!
I was looking for an explanation on the difference between "could" and "could have", and I came across this one.
Thank you very much for this clear and detailed explanation, but I think I'm still confused about the use of "could" when it is used to talk about "possibilities".
I mean "could" is the past form of "can" , then why is it used to talk about "possibilities" in the Present or in the
Future ? isn't it so confusing!
and sir, "could" can be used for both "abilities" and "possibilities" (as far as I have seen), but, by looking at a sentence, how can we recognize whether it(could) is showing "an ability" or it is talking about "a possibility"?. Is there a way to make
distinction between "could being used for an ability" and "could being used for a possibility" ??
Thanks! and waiting for your reply, sir :-)

Fivejedjon · Answer

JOMBI mean "could" is the past form of "can" , then why is it used to talk about "possibilities" in the Present or in theFuture ? isn't it so confusing!

It is perhaps more useful to think of 'could' as the distancing form of 'can'. It can distance in:

Time: I can play the piano.
I could play the piano when I was ten.

Reality: If John is here tomorrow, he can drive you to the station.
If John were here now, he could drive you to the station.

Directness: Can you lend me £10, please?
Could you lend me £10, please?

JOMB · Answer

Thank you very much for your reply sir, though It didn't clear my doubt about "when to use could to talk about a possibility" .
Let's see if I've got your point('could' as the distancing form of 'can');
here is an example;
If I say "I can visit my friend John Tomorrow"( I'm sure/ certain that I will visit . . .. )
But If I say "I could visit my friend John Tomorrow" (I'm NOT that sure/ certain. "COULD" here is weaker than "CAN"; It's less likely that I will visit him/ her . . . . )
am I correct sir ?

Anonymous · Answer

please reply about would and would have im also waititing for reply sir CJ

Anonymous · Answer

sir what a detailed discription u have given to all those questions that had troubling me alike,,,,thank you <img class='emoticon' style='Width:19px;Height:19px;' data-delaysrc='https://uat-englishforward-forums-backend.s3.us-west-2.amazonaws.com/Emoticons/21.gif' src='https://uat-englishforward-forums-backend.s3.us-west-2.amazonaws.com/Emoticons/21.gif' alt='Emotion: yes'/>

LeGion12359 · Answer

CalifJimThe situation is bad, but it could be worse. ~ ..., but worse situations [are / would be] possible.The situation is/was bad, but it could have been worse. ~ ..., but worse situations [are / were / would be] possible.These two are quite close in meaning. In the first, the speaker is more focused on the situation as it stands. In the second, the speaker may be more focused on the factors that brought about the situation.

I am sorry to teleport you back to few years from now

.But, I have a problem here, which is really pressurizing my head.
How can this be possible? The situation is so bad,but it could have been worse. [are/would be]. I think we use 'could+infinitive' only for present/future possibilities instead of 'could have+past participle'.
By the way, You really did justice with this 'could usage' summary. May *** bless you for this, Amen.

Differences between "could"/"could have" and "Would"/"would have" in the past?

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