1. MODAL VERBS OF
OBLIGATION

2. MODALS VERBS SON AQUELLOS VERBOS QUE FUNCIONAN COMO
AUXILIARES, YA QUE NO PUEDEN FUNCIONAR COMO VERBO
PRINCIPAL, ES DECIR, NO FUNCIONAN SIN OTRO VERBO. ESTE OTRO
VERBO SIEMPRE VA DESPUÉS DEL VERBO MODAL, Y ESTÁ EN FORMA
BASE (INFINITIVO SIN “TO”).
Present Positive Negative
have to /
don't have to
•strong obligation
(possibly from
outside) Children have
to go to school.
(sometimes 'have got
to')
•no obligation
I don't have to work
on Sundays.
•
You don't have to eat
anything you don't
like.
must / mustn't •strong obligation
(possibly based on the
speaker's opinion) I
must study today.
•negative obligation
You mustn't smoke
here.
should / shouldn't
•mild obligation or
advice You should
•mild negative
obligation or advice

3. Have to
► Se trata de una obligación en general
► Se usa para hablar de leyes, reglas, normativas…
►La obligación no procede de la persona que habla, sino de un tercero.
Se usa preferentemente para hablar acerca de una obligación impuesta
desde afuera, externa a nosotros.
► Va seguido del infinitivo sin “to”
►La forma interrogativa es: do / does + sujeto + have to+ infinitivo
► En la 3º persona del singular es has to
► Se suele emplear para el presente y futuro.
► En pasado se utiliza: had to + infinitivo sin “to”

4. Must
►Va seguido de infinitivo sin “to”
►Se usa para el presente
►En pasado: had to + infinitivo
►Recuerda que must have to + participio hace referencia a deducciones
o especulación en pasado.
►Examples:
“You must do your homework every night.” (Because I say you must!
“I must stop smoking!” (Because I think it’s a good idea to stop.)

5. AUSENCIA DE OBLIGACIÓN ( lack of obligation)
Dont or doesn´t have to
Dont or doesn ´t need to
►Ambas van seguidos de infinitivo sin “to”
►Se refiere a que no es necesario hacer algo, pero si quieres, puedes
hacerlo.
Prohibición ( prohibition)
Mustn´t
►seguido de infinitivo sin “ to”
► Se refiere a que algo está prohibido, no está permitido o que es
una mala idea.
DAR CONSEJOS ( give advice)
Should
►Se usa para dar consejos

6. Past Positive Negative
had to / didn't have to •obligation in the past I
had to wear a school
uniform when I was a
child.
•no obligation in the
past We didn't have to
go to school on
Saturdays.
must* changes to 'had to' -
should have + pp /
shouldn't have + pp
•a past action which
didn't happen: the
advice / regret is too
late You should have
gone to bed earlier, now
you have missed the
train.
•a past action which
didn't happen: the
advice / regret is too
late You shouldn't have
taken that job., it was a
bad idea.

7. EXAMPLES
In england you have to pay taxes
Children have to go to school
“You must do your homework every night.”
“I must stop smoking!”
“You don’t have to bring the food on the trip, we will bring
it”
“I don’t need to pay now. I can pay later.”
“You mustn’t play there because it´s very dangerous”
“He mustn’t eat peanuts. He’s allergic to nuts.”
“You should study hard so you can pass the exam.”
“He should see a doctor.”
“You shouldn’t smoke. It’s bad for your health.”