In "have to" and "ought to", "to" is part of the modal verb or the full infinitive that follows?

Answer 1

It's part of the full infinitive that follows.

Believe it or not but 'have to' isn't actually a modal verb. Although it's usage is very similar.

Think of some other modal verbs: can, could, shall, should, must (and the negatives of each one) - we can't put 'to' after them. That's why 'to' is not part of modal verbs in general.

I hope this has helped.

Answer 2

Here are the essential characteristics of modal verbs:
1. they have only one form (I, you, he, she can/might/may/must/should, etc.);
2. they usually do not indicate the time of the action (may, can, should, etc.); however, there are 2 exceptions ("could" and "might"); both refer to the past;
3. they go in front of the subject in questions ("Can we ...?");
4. they form the negative by adding "not" after them ("he cannot ...");
5. one should never use two modals together ("*you will can ...").

There are 2 groups of modals:
1. without "to" (can/could/may/might/should + go);
2. with "to" ("ought" + to go).

The difference between "have to" and "must" (both meaning obligation, necessity) is that the latter is a modal, and the former is not. Why? Because "to have + to-infinitive" is an ordinary verb (have/ has). As such, it does have past and future forms (had/will have). Also, in the interrogative and negative, you add the appropriate auxiliaries "do (not)/ does (not)/did(not)".

Answer 3

"Have to" and "ought to" are similar in meaning to the modal verbs "must" or "should" but not in structure. Many linguists would question the use of the term "infinitive" when talking about English. The term is really derived from Latin and other European languages which have this distinct form (parler - French) (sprechen - German). It is clearer to talk about the basic form of the verb. After all you look up "speak" in the dictionary, not "to speak", whereas you look up "parler" in French or "sprechen" in German.

Answer 4

An infinitive is a TO + a verb.