some similarities with modal auxiliaries in that it is invariant and defective in form and can follow auxiliary-verb syntax: it is possible to form questions like Used he to come here? and negatives like He used not (rarely usedn't) to come here. More common, however, (though not the most formal style) is the syntax that treats used as a past tense of an ordinary verb, and forms questions and negatives using did: Did he use(d) to come here? He didn't use(d) to come here. Note the difference in pronunciation between the ordinary verb use and its past form used (as in scissors are used to cut paper), and the verb forms described here: . The verbal use of used to should not be confused with the adjectival use of the same expression, meaning "familiar with", as in I am used to this, we must get used to the cold. When the adjectival form is followed by a verb, the gerund is used: I am used to going to college in the mornings. Deduction In English, modal verbs as must, have to, have got to, can't and couldn't are used to express deduction and contention. These modal verbs state how sure the speaker is about something. You're shivering—you must be cold. Someone must have taken the key: it is not here. I didn't order ten books. This has to be a mistake. These aren't mine—they've got to be yours. It can't be a burglar. All the doors and windows are locked. Double modals In formal standard English usage, since modals are followed by a base verb, which modals are not, modal verbs cannot be used consecutively. That requirement then dictates they can be followed by only non-modal verbs. Might have to is acceptable ("have to" is not a modal verb), but *might must is not, even though must and have to can normally be used interchangeably. Two rules from different grammatical models supposedly disallow the construction. Proponents of Phrase structure grammar see the surface clause as allowing only one modal verb, while main verb analysis would dictate that modal verbs occur in finite forms. A greater variety of double modals appears in some regional dialects. In English, for example, phrases such as would dare to and should have to are sometimes used in conversation and are grammatically correct. The double modal may sometimes be in the future tense, as in We