The conjugation of a verb is the regular arrange­ment of its several modes, tenses, voices, numbers, and per­sons. For regular verbs, the only tenses that have inflectional that is internal to the main word in the verb are the present and the past tenses. All other tense changes are made using auxiliaries.
In adding s or es, observe the same rules as in the formation of the plural of nouns:

For example

Plural play relates to singular plays.
Plural fly relates to singular flies.
Plural go relates to singular goes. Also, observe the rules for the changes of the regular verbs.

For example

The present verb drop has the past and past participle dropped.
The present verb reply has the past and past participle replied.

The principal parts of a verb are the present indica­tive, the past indicative, and the past participle. The present indicative and the past indicative are normally known as simply the Present and Past.
The principal parts of a verb are the present indicative, the past indicative, and the past participle. The present indicative and the past indicative are normally known as simply the Present and Past.

Principal Parts of Some Verbs

Infinitive	Present Indicative	Past Indicative	Past Participle
to reply	reply	replied	replied
to smile	smile	smiled	smiled
to sit	sit	sat	sat
to go	go	went	gone
to sing	sing	sang	sung

At this point proceed to Exercise 24.