The basic forms of the verb in Modern English are: the Infinitive, the Past Indefinite, and Participle II.

According to the way in which the Past Indefinite and Participle II are formed, verbs are divided into three groups: regular verbs, irregular verbs, and mixed verbs.

Regular verbs form the Past Indefinite and Participle II by adding – ed to the stem of the verb, or only – d if the stem of the verb ends in – e.

to want — wanted
to open — opened
to unite — united
to live — lived

#1. The following spelling rules should be observed:

Final y is changed into i before the addition of -ed if it is preceded by a consonant.

to carry — carried
to reply — replied

у remains unchanged if it is preceded by a vowel.

to enjoy — enjoyed

If a verb ends in a consonant preceded by a short-stressed vowel, the final consonant is doubled.

to stop — stopped
to plan — planned
to sob — sobbed
to stir — stirred
to submit — submitted

The final r is doubled if it is preceded by a stressed vowel.

to occur — occurred
to prefer — preferred
to refer — referred

The final r is not doubled when preceded by a diphthong.

to appear — appeared

Final l is doubled if it is preceded by a short vowel, stressed or unstressed:

to compel —compelled
to quarrel — quarrelled

Here belong the following groups of verbs:

#1. verbs that change their root vowel.

to sing — sang — sung
to meet — met — met
to win — won — won

#2. verbs that change their root vowel and add – en for ParticipleII.

to speak — spoke — spoken
to write — wrote — written
to take — took — taken

#3. verbs that change their root vowel and add – d or -t.

to sell — sold — sold
to bring — brought — brought

#4. verbs that change their final – d into – t.

to send — sent — sent
to build — built — built

#5. verbs that have the same form for the Infinitive, Past Indefinite, and Participle II.

to put — put — put
to set — set — set
to shut — shut — shut

#6. verbs whose forms come from different stems.

to be — was, were — been
to go — went — gone

#7. special irregular verbs.

to have — had — had
to make — made — made
to do — did — done

#8. defective (anomalous) verbs.

can — could
must
ought
may — might
will — would
shall — should

Their Past Indefinite is of the regular type, and their Participle II is of the irregular type:

to show — showed — shown
to sow — sowed — sown