MODALS

SHOULD-MUST-HAVE TO-CAN-COULD

These verbs add special meanings to the sentences:
Ability, permission, suggestions, advices, prohibition...

• You use them followed by an infinitive without "to".

           I should run to go to school.
           You must run to go to school.
           He can run to go to school.
           We could run to go to school.
           They have to run to go to school.

• You add "NOT" to make negative clauses:

            should + not = shouldn't
            must + not = mustn't
            could + not = couldn't
            can + not = can't // cannot

• You don't add "-s/-es" to the third person.

               I/You/He/She/It/ We/You/They
                                     + 
              SHOULD-MUST-HAVE TO-CAN- COULD