1. Can-Can't
   1. Expresa habilidad o posibilidad de hacer algo y se usa para pedir permiso.
   2. Afirmativa; suj+can+verbo Negativa; suj+can not+ verbo Interrogativa; can+suj+verb
      1. Ejemplos... (af) I can go to the swimmingpool. (neg) Mery can't run. (int) Can I close the door?
2. Could-Couldn't
   1. Expresa habilidad y posisbilidad en pasado de forma más educada que "can".
   2. Afirmativa; suj+could+verbo Negativa; suj+couldn't+verbo Interrogativa; could+suj+verbo
      1. Ejemplos... (af) Andrea could skate. (neg) Andrea couldn't skate. (int) Could you lend the biciclete?
3. Will- would
   1. Anuncia acciones o hechos futuros, predice lo que se cree que ocurrira y expresa acciones repentinas.
   2. Afirmativa; suj+aux will+verb Negativa; suj+will+not/won't+verb Interrogativa; will+suj+verb
      1. Ejemplos... (af) I would like to play tennis on Sundays. (neg) If he was the president, he would not raise taxes. (int) Would this work be finished by 4:00 PM.
4. must-mustn't-have to
   1. (must) Expresa una obligación que te pones a ti mismo. (mustn't) Expresa una prohibición de una ley. (have to) Expresa una obligación por ley.
   2. (must-mustn't) [af]; suj+must +verb [neg]; suj+mustn't+verb [int]; must-mustn't+suj+verb (have to) [af]; suj+have-has to+verb [neg]; suj+don't-doesn't have to+verb [int]; do-does+suj+have to+verb
      1. Ejemplos... (af) She must return later. (neg) He mustn't feel better later. (int) Does she has a boyfriend?