English Grammar - Sharon B. Clark - Bog

he person and number of a verb are those modifications in which it agrees with its subject or nominative. In each number, there are three persons; and in each person, two numbers: thus,

Singular. Plural. 1st per. I love, 1st per. We love, 2d per. Thou lovest, 2d per. You love, 3d per. He loves; 3d per. They love.

Where the verb is varied, the second person singular is regularly formed by adding st or est to the first person; and the third person singular, in like manner, by adding s or es: as, I see, thou seest, he sees; I give, thou givest, he gives; I go, thou goest, he goes; I fly, thou fliest, he flies; I vex, thou vexest, he vexes; I lose, thou losest, he loses.

Where the verb is not varied to denote its person and number, these properties are inferred from its subject or nominative: as, If I love, if thou love, if he love; if we love, if you love, if they love.