must, have to, should

must

You can use must to give your opinion or say that something is necessary

I haven’t spoken to my mother for ages. I must phone her

Must is used in written rules and instructions

Applications for the job must be received no later than 23 April

have to

I have to do something – It is necessary to do it. I am obliged to do it

You have to be over 21 to drink alcohol in the USA

According to the law, you have to drive with no more than 50 miles an hour

should

You can use should to give advice

You should exercise more if you want to keep fit

You should take vitamins during winter

You can use should when something is not right or what you expect

I wonder where Tom is. He should be here by now

Remember: should is not as strong as must or have to