The term anomalous finites refers to the group of 24 finites given below:
Is, am, are, was, were
Has, have, had
Do, does, did
Will, would; shall, should; can, could; may, might; must, ought, need, dare, used
As you can probably see, these are all auxiliary verbs. Some of them are also used as principal verbs. As auxiliaries their function is to help principal verbs to form their tenses and moods. As anomalous finites, they have other functions.
Anomalous finites are irregular. They do not form the past tense by the addition of -ed, -d or -t, but by a change in the root vowel. Some anomalous finites (must, ought) have no past tense forms at all. But these irregular finite verbs are different from other finite verbs in many respects and hence they are called anomalous finites.
The most obvious difference between anomalous finites and other finites is that they can be used with the contraction n’t which is the shortened form of not.
It isn’t true. (= It is not true.)
We aren’t going anywhere. (= We are not going anywhere.)
You shouldn’t do that.
I don’t know what to do.
Of the 24 anomalous finites, the forms be, have, do, need and dare are sometimes used as principal verbs and sometimes as auxiliaries. The remaining are always used as auxiliaries.
The use of anomalous finites
To form negative sentences
I know him.
I don’t know him. (NOT I know not him.)
She wrote to me.
She didn’t write to me. (NOT She wrote not to me.)
Here the anomalous finites do and did help to change positive statements into negative statements. The mere addition of not to the positive sentence is not enough in modern English.