網頁前端新手上路辛酸史

Obligation/Necessity                    Not Necessity

must                                                      don't have to

have to

have got to 

shall (in legal documents)

Permission                                   Prohibition(no permission)

may

can

could                                                  +NOT

be allowed to 

be permitted to

                                                           must not

Ability/Permission

can (present)

could (past)

be able to (past/present/future)

Expectation

be supposed to

Advice

should

ought to  

had better (serious;negative consequence)

Deductions/Conclusion

must