Q:

"You are" vs "you is" when "you" is used as both singular and plural?

The word "you," when used in a sentence, is always used as "you are" rather than "you is". This happens regardless of whether the speaker is speaking to one person or many. Is "you are", when applied to a single person, an example of the numerous exceptions in the English language? Is there ever a situation where it is appropriate to use "you is"?

A:

All English verbs except the full modals have three finite forms (finite forms are those which have tense, number and person):

one form for present tense, 3d person singular ... full modals lack this form
one form for present tense, all other persons and numbers  
one form fall past tense, all persons and numbers

The verb be, and only that verb, has two additional forms

one form for present tense, 1st person singular: am 
one form for past tense, 1st and 3rd person singular: was

Here is a comparison of conjugations for be, love, and the full modal may:
PRESENT
        I AM     we are                I love      we love            I may      we may
      you are   you are              you love     you love          you may     you may
he/she/it IS   they are        he/she/it LOVES   they love    he/she/it may    they may

PAST
        I WAS    we were               I loved     we loved           I might    we might
      you were  you were             you loved    you loved         you might   you might   
he/she/it WAS  they were       he/she/it loved   they loved    e/she/it might  they might

So you are is not an exception; the exceptions are I am and I was. You is is not possible.
English used to have a distinct second person singular pronoun, thou, but dropped it in the course of the 16th and 17th centuries. It had its own verb forms,too (endings in -st, except be had the form thou art); but happily those were dropped, too; so there's that much less you have to to learn.

