THE MODAL VERBSHAVE TO, DON´T HAVE TO-SHOULD,OUGHT

HAVE TO REFERS ABOUT OBLIGATION OR SOMETHING THAT IT´S NECESSARY TO DO.

She has to clean the floor

I have to feed my dog

HE SAYS I HAVE TO DO MORE EXERCISE(HE SAYS IT IS NECESSARY FOR ME TO EXERCISE MORE)

SHOULD IS USED TO GIVE ADVICE OR EXPRESS SOMETHING THAT IS A GOOD IDEA. CAN BE USED FOR GENERAL SITUATIONS AS WELL AS SPECIFIC

You have a headache. You should take an aspirin.

You should always consult a doctor before taking antibiotics

OUGHT TO

This verb is used in the same way as Should. It expresses a weak obligation.

Karen ought to be more careful

We ought to go together