Dic: should (giving opinions that you are not certain about)

■ You use should in expressions such as I should think and I should imagine to indicate that you think something is true but you are not sure.

• I should think it's going to rain soon...

■ used with I and we to give opinions that you are not certain about.

• I should imagine it will take about three hours.
• “Is this enough food for everyone?” “ I should think so.”  
• “Will it matter?” “ I shouldn't think so.”

■ [I should think/imagine/hope]

spoken. a) used to say that you think or hope something is true, when you are not certain.

• I shouldn't think they've gone far.
• 'I suppose there'll be a lot of complaints?' 'I should imagine so.'

b) used to emphasize that you are not surprised by what someone has told you because you have moral reasons to expect it.

• 'She doesn't like to hear me swearing.' 'I should think not.'
• 'He did apologize.' 'I should hope so, after the way he behaved.'

.... COBUILD, OALD, LDOCE

CF.

■[PAST INTENTIONS/EXPECTATIONS] used as the past tense of 'shall' after 'I' or 'we' to say what you intended or expected to do.

• We knew that we should be leaving the next day.

■[IMAGINED SITUATIONS] formal. especially BrE. used after 'I' or 'we' to say what you would do if something happened or was true

• If anyone treated me like that, I should complain to the manager.
• I should be surprised if many people voted for him.

■ [EXPECTED THING] a) used to say that you expect something to happen or be true

• It should be a nice day tomorrow.
• Try phoning Robert - he should be home by now. 
• Australia should win this match.
• 'Artistic people can be very difficult sometimes.' 'Well, you should know - you married one.'

.... LDOCE

■ You use should when you are saying that something is probably the case or will probably happen in the way you are describing. If you say that something should have happened by a particular time, you mean that it will probably have happened by that time.

• You should have no problem with reading this language...
• The doctor said it will take six weeks and I should be fine by then...

..... COBUILD