You shouldn't say anything.

• It's not a good idea to say anything

• It's forbidden to sa anthing.

You mustn't say anthing.

• I say you're not allowed to say anything.

• It's not necessary to say anything.

This can't be the right way.

• I'm sure that this isn't the right way.

• Perhaps this isn't the right way.

You don't have to tell him.

• It's not necessary to tell him.

• It's prohibited to tel him.

That must be Tim at the door.

• Perhaps that's Tim at the door.

• I'm sure that's Tim at the door.

It can snow in March.

• It's possible for it to snow in March, it sometimes happens.

• Perhaps it will snow in March.

The match could be postponed.

• Perhaps the match will be postponed.

• Perhaps the match was postponed.

There is a globe on teacher's table.

• They can't be in a geography class.

• The could be in a geography class.

It's necessary to do this.

• You need to go to the office, now

• You can go to the office, now.

This is not allowed.

• She doesn't need to enter the premises.

• She mustn't enter the premises