“Should” for Obligation
Should expresses an obligation that is not as strong as Must.
Sometimes Should is used instead of Must to
make rules, orders or instructions sound more polite. This may appear more
frequently on formal notices or on information sheets.
Example: On
hearing the fire alarm, hotel guests should leave their room
immediately.
Example: Passengers should check
in at least 2 hours before departure time.
All of the above example
sentences can have must instead of should making
the obligation stronger and less polite.
