[General] Should be absent/were absent

I am learning the usage of 'should' and one usage says:

The teacher was astonished that 10 students should be absent today.

The book says it means 'the teacher was astonished that 10 students were absent today', but the word 'should' stresses the degree of the astonishment. Is the explanation right in your opinion?

Thank you in advance.

Yes. Exactly right. The "should" expresses a more unlikely case than the simple past, and therefore the teacher's astonishment is even greater.

Note the three hypotheticals, in decreasing probability:

1. If ten students are absent (at least as likely as the students' presence)
2. If ten students should be absent (a possibility)
3. If ten students were to be absent. (a more hypothetical possibility)

In the construction with "that", "were to be" is not an option, but "that 10 students were absent today" is still less probable than "that 10 students were [=past of are] absent today".

I should think the less likely the event, the greater the astonishment -- and the greater the astonishment, the less likely the event. Otherwise why be astonished at all? Ten absences certainly require greater explanation than two!

In other words, the "should" connotes both how improbable ten absences are, AND the teacher's astonishment -- just as LiuJing's textbook says, and in perfect agreement with the order of decreasing probability I quoted.

Gillnetter said:

I would understand "should" in this context to mean that the teacher was astonished that such an event would occur. I don't see how the degree of astonishment is referred to here, it is pointing more to the fact that such a large number of students were not in attendance.

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Can I rephrase it to mean the same by: the teacher just couldn't believe the fact that ten students were absent today.

LiuJing said:

Can I rephrase it to mean the same by: the teacher just couldn't believe the fact that ten students were absent today.

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Yes.

No.
You could say greatly surprised that so many students were absent but not change it to disbelief.

"I can't believe" is a common enough colloquialism that really just means "i am shocked" or "I am very surprised". Astonishment and disbelief overlap.

Yes.

abaka said:

"I can't believe" is a common enough colloquialism that really just means "i am shocked" or "I am very surprised". Astonishment and disbelief overlap.

Yes.

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It's not suitable in the context of the English classroom.