MODALS

• Modals


  Are auxiliary or helping verbs. They may be used in expressing permission, obligation and prohibition.
• Permission


  Is an act of giving consent or authorization. In stating permission, modals to be used include can, could may.
• Can


  Is used to ask for and give permission.
• Could


  Is also used as a more polite and more formal modal in asking permission (May not be given)
• May


  Is the most polite and formal modal used in asking and giving permission.
• Prohibition


  Is the act of disallowing or prohibiting someone in performing or doing something. Modals showing prohibition include can't and must not/mustn't.
• Can't 


  Used in dealing with something against the rules, laws and signs. This is used when the speaker is not the one who sets the rules.
• Must not/mustn't


  Used in dealing with something that is not permitted.
• Obligation


  Expresses commitment or duty. Modals used in expressing obligation include have to (has to) and must.
• Has/Have to


  Used when obligation comes not from the speaker. The obligation is set by an authority, rule or law.
• Must 


  Used when expressing obligation comes from the speaker or from an authority.
• No obligation


  Expresses the absence of commitment or duty as one may do it or not. Don't (doesn't ) have to is used to express no obligation.