According to Eckersley, the verb is “the part of the speech by which we are able to say what a person or animal or thing is, or does, or what is done to that person, animal, or thing”.
The Oxford English Dictionary says that the verb is the part of the speech which is used to express action or being.
It is not difficult to distinguish this part of the speech, but there are some difficulties when we try to define the class. There are different criteria to define verbs.
1 According to form:
They take the suffix -s in the third person singular present, and the suffix -ing for the present participle, but it doesn´t affect to the modal verbs.
They have different forms for present and past, but it doesn´t affect verbs like cut, put, or hit.
2 According to function:
They could be defined as the sentence forming elements of a group, however, this definition doesn´t comprise infinitives, gerunds, and participles.
THE MORPHOLOGY OF THE ENGLISH VERB
Most English verbs have 4 forms: walk
modals have 1 or 2 forms: must, can/could
some verbs have only 3: put, puts, putting
some verbs have 5: drink drank drunk drinks drinking
the verb to be has 8 forms: be is are am was were being been
THE STEM OR BASIC FORM:
THE STEM PLUS SIBILANT SUFFIX
/iz/ after sibilants
/z/ after voiced
/s/ after voiceless
es after sibilants, washes, dresses
es after single o: goes, does
ies after consonant