Examples of errors:
Should has the following meanings:
1. Should is used in British English as the past tense of shall (first person only, cf. above, shall in sense 1) in the main clause of unreal conditions and in indirect speech. This usage is exactly parallel to will/ would in the second and third person, and in all persons inAmerican English. For example:
If it rained we should get wet.
He told me I should hear from him the next day, but I didn't.
In the second example, should is ambiguous in that it can also be understood as equivalent to ought to.
2. Should is completely synonymous with ought to expressing desirability or probability. In both cases the meaning is parallel to must, though less emphatic, e.g.:
You should/ought to study harder .(desirability)
You must study harder (desirability, emphatic)
They should/ought to be there by now (probability)
They must be there by now (probability, emphatic)
In the first sentence should or ought to are equivalent to 'It would be better if you studied harder', whereas must is equivalent to 'It is necessary that you study harder',' In the second sentence should/ought to is equivalent to 'They are probably there by now', whereas must expresses a stronger degree of probability, i.e. 'They are most likely (almost certain) to be there by now.
3. What Quirk et al. (1972:§3.46, 11-729 12-35 ff.) call the "putative" use of should occurs in that clauses,, particularly after expressions of emotion, e.g.:
It's a pity
I'm surprised
it's disgraceful
It's unthinkable
It worries me
that he should resign
Should in itself leaves the factual status of the predication (here, whether or not he actually resigned) in question, though context may make this clear. Compare:
"Mr. Hawks is going to resign on Thursday."
"Oh really? He's such a capable man; I'm surprised that he should resign."
and
"Mr. Hawks may resign on Thursday.
"Oh really? 'He's such a capable man; I'm surprised that he should resign.
Should in the first conversation is replaceable by is going to or will, since the future event is relatively certain. In the second conversation should is not replaceable by is going to or will, since the future event is only a possibility. In both cases should indicates surprise at the putative idea of resigning rather than at the event of resigning itself. This use of should also occurs in certain idiomatic questions and exclamations, e.g.:
How should I know?
Why should he be resigning
That he should dare to attack me!
Who should come in but the mayor himself!
4. Should is used in the if clause of real conditions to indicate some tentativeness, i.e. a slight degree of doubt in the mind of the speaker, concerning the likelihood of the condition being fulfilled. This type of sentence is thus somewhere between a real and unreal condition, though based on the tense usage in the main clause it is usually a real condition. For example, in
If it should rain tomorrow, the picnic will be ruined.
should indicates the speaker thinks it somewhat more unlikely that it will rain than the completely neutral
If it rains tomorrow the picnic will be ruined.
Nevertheless, should does sometimes occur in the if clause of unreal conditions, e.g.:
If there should be a hurricane, our house would be devastated.
In all of these cases, inversion of should is possible, resulting in a more formal tone:
Should it rain tomorrow, the picnic will be ruined.
Should there be a hurricane, our house would be devastated
Should in sense 2 has present or future time reference, so it is obviously incorrect in'(1), where the main verb (waited) is in the simple past. Should in sense 2 has no morphological past tense counterpart, but past time reference can be expressed with the perfect infinitive, e.g.:
You should do it (today, tomorrow)- while you still can.
You should have done it (yesterday) while you still could.
The perfect infinitive construction,, however, implies that what should have occurred in fact did not:
You should have done it (but you didn't).
This implication is incorrect in (1) because the train did in fact take her home. Should have been in (1), by implying that the story was in fact not funny, also implies that some sort of story was written--otherwise the judgement as to its humor or lack of same would not be possible. What the author intended to say, though was that the story was supposed to be funny, but, he did not actually write anything at all. Be supposed to, unlike should have been, does not imply that any story was written:
The story was supposed to be funny, and it was.
The story was supposed to be funny, but it wasn't.
The story was supposed to be funny, and he wrote a hilarious one.
The story was supposed to be funny, but he didn't write one at all.
After be supposed to, since the inflected form of be already indicates past tense, the perfect infinitive is optional:
It was supposed to be funny.
It was supposed to have been funny.