Shall and Should
In modern English, "shall" is mostly used for questions.
Examples: Shall I get some steaks for tonight? Shall we dance?
"Should" is used to recommend something.
You should really stop wearing heavy metal T-shirts to job interviews.
They shouldn't be so hard on him.
Would"Would" can be used for polite questions, or if you want to do something but unfortunately can't.
Would you like a piece of fresh gooseberry merengue pie?
I would love to taste your pie, but unfortunately I'm diabetic.
May and Might"May" is used for very polite questions, for things you are allowed to do, and when you think: "Maybe I will do this, but I'm not sure."
May I take your coat, Madame?
You may go outside after you finish your homework.
I may mow the lawn before lunch.
"Might" is used when it is possible that something is going to happen.
They might team up against us.
She might go to the theater tonight - you never know!
Can and Could"Can" is used when you ask or get permission for something, when you are able to do something, and when something is possible.
Hey Cat, can I use your lipstick?
The new material can be used in the kitchen, in the bathroom, or outdoors.
I can do 20 press ups in one go - how about you?
"Could" is used to ask a polite question or if something is not done, although it is possible. It is also used for suggesting something.
Could you help me clean the kitchen please?
I could take the garbage with me later.
You could tell her to stop calling you.
Must and Must not"Must" is used when something has to be done. "Must not" is used when it should definitely not be done because it is not allowed, bad for you, dangerous, illegal, or sinful.
This cake is scrumptious. You must give me the recipe!
I love it, but I must not eat too much of it.