VERBS w/o S endings

[crsommers]

Does anyone know the rule for why some verbs, depending upon the pronoun preceding it, do or dont take an S??

As in:

I sit
You sit
They sit
We sit
She sits
He sits

Thanks/carol

[Tdol]

In the simple present, the third person singualr (he/she/it) takes the -s, except for modal verbs (can/must/may, etc).