Learn English – Why do they say “may not” for things which people shouldn’t do


I have seen in so many place where they would have mentioned "You may not.." etc for the things people shouldn't do. For eg: in companies where USB is not allowed, they will mention like this "You may not use USB/CD etc", similarly "You may not download free softwares", "You may not tailgate the doors" etc.

These all things should be like this right "You should not use USB/CD etc", "You should not download free softwares" etc, this "May not" seems like saying "optional" it may indicate like "people may follow" etc

Can anyone guide me in this? I always get confuse in this.

Best Answer

In this context, may means that you have permission to do something, so may not means you are not permitted to do something.

should is generally interpreted less strictly, as describing a desire or strong suggestion, rather than a requirement. So should not means that they would prefer or recommend you not do something, not that it's prohibited. For example, You should not go swimming during a thunderstorm.

Sometimes these can be conflated, though. You should not drive above the speed limit, because it's against the law and you might get a ticket.

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