Cambridge Grammar of English Hardback with cd-rom a comprehensive Guide

SEMI-MODAL VERBS

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The semi-modal verbs are: dare, need, ought to and used to. (Dare and need are

also lexical verbs.)

These verbs are also sometimes called ‘non-typical’ or ‘marginal’ modal verbs.

In some ways they behave grammatically like lexical verbs; in some ways they

behave grammatically like the core modal verbs:

I 

dare not tell her what’s happened.

(as with core modal verbs, negative formed without auxiliary do)

Marie 

didn’t dare say anything to them.

(as with lexical verbs, negative formed with auxiliary do)

We 

ought to wash this tray, oughtn’t we?

(unlike core modal verbs, followed by to; like core modals, can be used in a tag

question)

Often the different behaviour marks a difference between formal and informal

styles:

I’ve learnt to become open-minded. I 

didn’t used to be. 

(negative formed with auxiliary do; the most common negative form of used to

in general contexts)

There is something rather secretive about Lucian at times. He 

used not to be

like that. He was such a frank sort of boy, if you know what I mean. 

(negative formed without auxiliary do, but only usually found in formal styles)