Phrasal modalsPhrasal modals are phrases which form a single verb group with another verb and which affect the meaning of that verb in the same way that a modal verb does. Some phrasal modals begin with be or have: be able to, be bound to, be going to, be liable to, be meant to, be supposed to, be sure to, have got to, and have to. The first word in these phrases changes its form depending on the Subject and the tense, in the way that be and have normally do. You say I am liable to panic and She is liable to panic, We have to leave tonight and We had to leave last night. The other phrasal modals do not change in this way. You say I would rather go by bus and He would rather go by bus.Most phrasal modals are made negative by putting not after the first word in the phrase, as in He is not able to be with us or You ought not to eat so quickly. However, had best, had better, would rather, would just as soon, and would sooner are made negative by putting not after the whole phrase, as in You had best not go by yourself or I would just as soon not go by myself. The negative of would do well to is made by putting not after well, as in She would do well not to forget that. The phrasal modal used to has three negative forms: used not to, didn't used to, and didn't use to.The interrogative of verb groups formed with most phrasal modals is made by placing the Subject after the first word in the phrase, as in Have you got to go? or Would you sooner stay? The interrogative form of have to is do you have to as in Do you have to go? The interrogative form of used to is did you used to, as in Did you used to eat sweets?Phrasal modals have the following patterns:
MODAL infI have to go.
MODALGo if you have to.
MODAL inf than/as infI'd rather die than surrender.
MODAL thatI'd rather you didn't.