Many peculiarities of the English verbs were developed during the Old English period and fixed in Middle English. The verbs were falling into two subclasses: finite and non-finite. The verb in its finite forms could possess the categories of person, number, tense, aspect voice and mood. The non-finite forms (Verbals) are the Infinitive, Participle I, Participle II and the Gerund. Verbals do not function as true verbs. [3] Verbals can function as nouns, adjectives, and adverbs.

English verbs are also classified into notional and structural. Notional verbs are so-called main verbs; they possess a lexical meaning on their own. Structural verbs (modals, link verbs and auxiliary verbs) do not have an independent syntactic function or lexical meaning. They are always connected with other words. Usually grammarians also distinguish so-called semi-notional verbs. These verbs can be used either on their own or as auxiliaries (start, stop, must, may, can).

Verbs are the base of any English sentence, so they are used frequently in the discourse. Aida Saakyan, Modern English grammarian, claims that the most frequent notional verbs of the English language are “to say” (4500 uses per million words), ‘to get”(3400 uses) and “to go” (3300 uses). Though the structural verbs are used more often. The diagram of English notional verbs’ frequency by Saakyan is given in Appendix 1.

We can see from the history of English that verbs have fallen into two groups according to their conjugation – weak regular verbs and strong irregular verbs. In Modern English the regular verbs is the largest group. The Past Simple form and Past Participle of these verbs are formed with the help of suffix -ed that originated from the fusion of two Old English affixes: base-forming -i- (-e-) and past tense forming    -d- (-t-).

There are nearly 500 irregular verbs in Modern English including the archaic ones. Online-source UsingEnglish.com even claims that there are 620 irregular verbs in total. [4] But in fact we use actively no more than 200 of them. Irregular verbs compose the past form according to the traditional patterns.

Though irregular verbs are said not to obey the general rules, they can be subdivided according to the patterns of their modification. In the present work I tried to divide them by convention into 13 groups:

Group 1.
The verbs that belong to this group have one and the same form in the Infinitive, Past Simple and Participle two.  Here are some examples from this group:

More examples are available in Appendix 2.

We can see that some words of this group, like, for example, to burst, nowadays accept the regular conjunction also
[1]:

Group 2.
The Past Tense and Past Participle forms of these verbs  are composed with the help of the flexion “-ought” (rarely – “-aught”).

The verb “to buy” also has an archaic form of Participle II – “boughten”.

Group 3.
The final consonant “-d” in the stem changes into “-t” in both forms.

Here some of the verbs can also accept the affix “-ed” in Modern English.

Group 4.
The root vowel “-i-“ changes into diphthong “-ou-”.

The words from this group have one more peculiarity – the letter “-i-“ is read here as [ai], though the syllable is closed. This helps, for example, to distinguish the verb “to wind” ([waind]) from the noun “wind” ([wind]).

The verb “to grind” accept the “-ed” inflection in Past Simple form.

Group 5.
The root vowel before “-ng” changes into “-u-“. Usually the root vowel is “-i-“.

Some verbs of this group are also becoming regular.

The verb “to sting” can accept two forms in Past Simple:

Thus, it can be also classified to Group 10 (see below).

Group 6.
The long [i:] changes into the short [e]. Some verbs of these group also accept the consonant “-t” or “-d-“ at the end of the stem.

The verb “to kneel” can also be used as a regular verb.

Group 7. The verbs save their vowel but accept the consonant “-t” (rarely – “-d-“) at the end of the stem. In some cases we can notice the reduction of vowels.

Most of these verbs can also be used as regular ones. In Group 7 this variation is more frequent than in the other groups.

Group 8. The Past Simple and Participle II forms do not obey the principles of the Groups 1-7, but they still coincide.

The verb “to strike” can also have another form in Past Participle. So it can be also classified as the verb of the Group 12.

Group 9. One of the forms coincides with the infinitive. It can be either Past Tense, or Past Participle.

The verb “to beat” can also be treated as the verb of Group 1.

Group 10. The root vowels change according to the pattern:

“-i- > -a- > -u-“. This group is the closest descendant of Germanic/Old English strong verbs (i-class).

Group 11. In the Past Simple form the verb changes the root vowel. Participle II has “-n-“ at the end of the stem; it also usually changed the root vowel.

Group 12. The Past Simple form does not coincide with the infinitive and with the Participle II. Participle II has “-en-“ at the end of the stem; its root vowel coincides with the infinitive’s root vowel.

Group 13. The Past Simple and Participle II forms do not obey the principles of any patterns. Here suppletive verbs can be found.

We can come to the conclusion that the structure of verb conjugation in Modern English aims at simplification. The verbs from six groups of thirteen show their tendency to accept affixation instead of root vowels alternation.

The most common pattern is the one of Group 8. Out of 140 words analyzed 20 verbs (14,29%) belong with this group. The frequency of patterns used for creating the past forms of the irregular verbs is shown in Appendix 3.