OBLIGATION

WE USE ...

WE USE CAN + INFINITIVE BE ALLOWED TO + INFINITIVE	TO TALK ABOUT THINGS THAT ARE PERMITTED  IN THE PRESENT
WE USE CAN’T + INFINITIVE NOT BE ALLOWED TO + INFINITIVE	TO TALK ABOUT THINGS THAT ARE NOT PERMITTED  IN THE PRESENT
WE USE HAVE TO                              + INFINITIVE HAS TO	TO TALK ABOUT THINGS THAT ARE NECESSARY TO DO
WE USE   DON’T                              HAVE TO + INFINITIVE   DOESN’T	TO TALK ABOUT THINGS THAT ARE NOT NECESSARY TO DO
WE USE COULD + INFINITIVE  WAS / WERE ALLOWED TO + INFINITIVE	TO TALK ABOUT THINGS THAT ARE PERMITTED  IN THE PAST
WE USE COULDN’T + INFINITIVE WASN’T / WEREN’T  ALLOWED TO + INFINITIVE	TO TALK ABOUT THINGS THAT ARE NOT PERMITTED  IN THE PAST
WE USE HAD TO + INFINITIVE	TO TALK ABOUT THINGS THAT ARE NECESSARY TO DO IN THE PAST
WE USE DIDN’T HAVE TO + INFINITIVE	TO TALK ABOUT THINGS THAT ARE NOT NECESSARY TO DO IN THE PAST

Future