1. Modal Verbs. Material Adicional Idiomas. Modal Verbs: Obligation & Recommendation - To express: obligation, no obligation, prohibition and recommendation - have to - must - should - ought to SOURCE: http://perso.wanadoo.es/autoenglish/gr.must.p.htm

2. Modal Verbs. TYPE 1: Obligation: a) have to E.g. Maria has to go to Rome. She had to see a doctor. (Use only have to in verb tenses apart from the present simple). b) must E.g. You must see a doctor. (Must expresses more urgency than have to). TYPE 2: No Obligation don't have to E.g. He doesn't have to go.

3. Modal Verbs. TYPE 3: Prohibition mustn't Eg. You mustn't insult people. TYPE 4: Recommendation a) should Eg. You shouldn't eat so quickly. b) ought to Eg. You ought to phone your mother. (Ought to is not used in the negative).

4. Modal Verbs. Further links: http://www.ompersonal.com.ar/omgrammar /verbosmodales1.htm http://www.perfect-english- grammar.com/modal-verbs-of- obligation.html http://perso.wanadoo.es/autoenglish/gr.mu st.p.htm