1 Words or expressions that express likelihood are: could, might, may, can, will. Those that express obligation are: not obliged to, (doesn’t) have to, needn’t, there’s no obligation to. Of these, could, might, may, can, will and need(n’t) are classified as modal verbs (or, more correctly, modal auxiliaries). To these can be added: can, would, shall, should and must.

2 The completed chart looks like this:

Examples of modal verbs with the bare infinitive are a – f.

Examples showing that there is no special third person form, i.e. adding -s, are a, b and f.

Examples showing not-negation are c and d.

Examples showing inversion in questions are h and e.

An example that shows how modal auxiliaries do not form sequences is g, where should must is not possible, so have to is used instead. Another example is f.

Lexical verbs, on the other hand, do not take the bare infinitive (apart from a few exceptions, like help): see examples h – k; they have a special third person form h, require an auxiliary verb for not-negation i and for inversion j, and can be preceded by auxiliaries k.

3 in the case of need, it behaves like a lexical verb in examples a, c and e. the features of auxiliary verbs apply only in questions and negatives, as in examples b and d. but even here there is some variability, as the examples c and e demonstrate. except for the fact that it is usually followed by the to-infinitive, not the bare infinitive, as in g, ought behaves in every respect like a ‘pure’ auxiliary, in that there is no third person form, and it is negated by adding not (as in example f). in some varieties of english, however, it can be treated like a lexical verb, (as in example h).

When use in the past tense is enlisted to talk about past habits, it normally functions like a lexical verb, as in example j, but in some registers of English the form used not to (rather than didn’t use to) attests to its modal origins, as in example i.