Language: Thee and Thou
This is not grammar you are taught in school, but simply the ordinary way people talk. Your excuse for incorrect usage cannot be that you were poorly educated.
When the next word begins with a vowel, use thine for thy:
I like thy face.
The "-st" ending is only used with "thou" and only with verbs.
I did see him go with thee.
The "-eth" ending is only used with he, she, and it.
He loveth best that loveth well.
Using Thou familiarly
Thou and thee are familiar or informal forms of you. You use it to address your children, your servants, your wife, your most intimate friends, your dog, and God. (Hey, who knows you better than God?)
Use the more formal you when addressing your parents, your master, your social superiors, your patron, your customers, your officers, and your horse, who may be worth as much as you are.
Don't panic: The familiar and formal forms (thou and you) get mixed in a sentence even in Shakespeare. But only downward or to an equal, never up.
That is, you might address your servant using both thou and you together, but he wouldn't do that to you. Anger and strong feeling, of course, cancel other conventions.
Still, his lordship may take offense if his tenant chats him up using "thou", or he may simply ignore it, but you never know!
25 March 2008 mps