must, have to, should

Tres modales para expresar obligación y consejo, cada uno con distinto grado de fuerza.

must

Obligación interna fuerte — lo siento necesario: I must call her.

have to

Regla o requisito externo — viene de fuera: I have to wear a uniform.

should

Consejo o recomendación — es una buena idea: You should see a doctor.

must vs have to

Obligación interna vs regla externa

must — yo decido

I must study tonight.

mi propia decisión

You must try this restaurant!

recomendación fuerte

have to — regla

I have to wear a helmet.

ley/regla externa

She has to start at 9.

regla de la empresa

En el inglés hablado cotidiano, have to y must suelen ser intercambiables. La diferencia importa más en escritura formal.

Negativos: diferencia crítica

mustn't vs don't have to — ¡significados opuestos!

mustn't = prohibido

You mustn't park here.

= NO está permitido

You mustn't tell anyone.

= prohibido

don't have to = no necesario

You don't have to come.

= opcional, tú decides

You don't have to hurry.

= sin prisa

Cuidado: mustn't = PROHIBIDO. Don't have to = NO REQUERIDO (pero sí permitido). Confundirlos cambia totalmente el significado.

should / shouldn't — consejo

Más débil que must — una buena idea, no una orden

Consejo

You should eat more vegetables.

Recomendación

You should see that film — it's brilliant.

Consejo negativo

You shouldn't stay up so late.

Pedir consejo

Should I call her?

ought to

Ought to = mismo significado que should (más formal).

had better — consejo urgente

Más fuerte que should — implica consecuencia negativa

had better + verbo base

You had better hurry — the train leaves in 5 minutes!

Contracción

You'd better call her now.

Negativo

You had better not be late.

"Had better" siempre lleva el verbo en forma base (no "had better to go"). Y aquí "had" no es pasado — se refiere al presente/futuro.

Errores frecuentes

You mustn't wear a uniform. (significado: no es obligatorio)

→

You don't have to wear a uniform.

mustn't = prohibido · don't have to = no obligatorio

You should to see a doctor.

→

You should see a doctor.

Los modales nunca llevan "to"

She musts go now.

→

She must go now.

Los modales nunca llevan -s

I have to study — it's my choice.

→

I must study — it's my choice.

Propia decisión → must, no have to

Resumen

must

obligación interna fuerte

I must study.

have to

regla/requisito externo

I have to wear a uniform.

should

consejo / recomendación

You should see a doctor.

mustn't

PROHIBIDO

You mustn't park here.

don't have to

NO OBLIGATORIO

You don't have to come.

Practicar ahora →

Modals: must / should