@centrox,
Quote:The original question is about an algebra problem expressed in words. It includes a situation in which some things which might have happened didn't happen, and how that would have affected a situation also in the past - if more or fewer people had joined the trip, they would have paid more or less money.
The original question is about a singular event that
uses the same language structures that are used to determine the usage for the billions/trillions of other possibilities that have the potential to exist.
Quote:In this situation, 'had' is correct, and 'would have' is not.
You keep saying this but that doesn't make it true.
Quote:I invented an example in which something that might have happened (I locked the door) simply didn't happen. As a result my house was burgled. Could/would/should are not possible as replacements for that.
Quote:Centrox: "Would have" for "had" is a very common (mainly US) error.
"If I would have locked the door, then the burglar would not have got in". The first "would have" is an example. It should be "had".
The real situation NOW, is that the lock is broken/non-functional so it is not a possibility to lock the door]
So, given this set of circumstances, a factual "had locked" is essentially nonsensical.
If I could have locked the door, then the burglar would not have got in.
"could have locked" is entirely possible.
If only I would have been able to lock the door, then the burglar would not have gotten in.
"If only I would have been able to lock the door" is also possible. It is more emotive than a "had ... ".
"If I should have locked the door" is not possible only because it isn't sensible.
Should he have been his usual sensible self and locked the door, then the burglar would not have gotten in.
Quote:If you want to invent scenarios in which these would have been, then you are welcome to do so.
That scenarios exist in which these can be used describes that the proscription against doing so is bogus. Certainly, as described, there are situations where an "if S would have ..." can't be used but that isn't for grammatical reasons, it's because it doesn't make sense.
Just as, all the following,
"If he may/should/shall/will/can have locked the door, then the burglar wouldn't have gotten in"
make no sense.