Modal Verb "Should be"

Hi, my name is Xabier I'm from Spain and I also am English Student, I have a question about the modal verb "Should be":

The quantity of fuel which is calculated to be necessary for a jet
aeroplane to fly IFR from departure aerodrome to destination aerodrome
is 5352 Kg. Fuel consumption in holding mode is 6000 Kg/H. Alternative
fuel is 4380 Kg.

Contingency SHOULD BE 5% of the trip fuel.

What is the minimum required quantity fuel on board for take off?”

I dont know how interpretate this question. Is "Shoul be" an obligation, advise, something god to do...? I am really confuse about it, I think is really umbiguos.

If is an obligation, it will be one asnwer, if is an advise, another answer will be correct.

I already check the dictionary and still not able to find the right meaning.

Hope someone can help me, my exam final result depend on this.

I would really apreciate if someone could help me.

Thanks a lot.

Kind regards


  • The PERSON of the SUBJECT is often a clue:

    • FIRST PERSON I should do it. usually means 'It's the right thing to do'. we often use I should to contrast with what we actually do: I should do it, but I don't.

    • SECOND PERSON You should do it often means 'I advise you to do it' but it can also mean 'It's the right thing to do'.

    • THIRD PERSON (human) He should do it usually means 'It's the right thing to do'. It sometimes means 'By my calculations, he'll do it'. It's very unusual to mean 'If he asked me I would advise him to do it'.

    • THIRD PERSON (non-human) It should do it often means 'If it's woking properly, it will do it'. Sometimes it means 'By my calculations it will do it'.

    In sentences with be it's little different

    • FIRST PERSON I should be the first often means 'If the right things are done, I'll be the first'. It can also mean 'By my calculation, I'll be the first'

    • SECOND PERSON You should be the first similarly can mean 'If the right things are done, you'll be the first' or 'By my calculation, you'll be the first'. An advice meaning is possible only if the hearer can control whether or not he/she is the first.

    • THIRD PERSON (human) He should be the first is like the SECOND PERSON meanings: 'If the right things are done, he be the first' or 'By my calculation, he'll be the first'. And advice meaning is possible but unlikely 'If he asked me I would advise him to be the first'.

    • THIRD PERSON (non-human) It should be the first usually can't have an advice meaning.

    Certainly we can't mean 'If the contingency asked me, I'd advise it to be 5%'.

    That leaves 'If the right things are done it will be the first' and 'By my calculations, it will be the first'.

    Of these two, the By my calculations meaning seems to be impossible in the problem you quote. The question-setter is asking for YOUR calculations.

    So I think it's safe to understand 'If the right things are done, contingency will be 5%' — which is an indirect way of saying that YOU should include that contingency in your calculations.

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