Thou is the subject form — it does the action: "Thou art my witness." Thee is the object form — it receives the action or follows a preposition: "I shall follow thee." They split the same way he and him do, or I and me.
The core difference
Both are the old singular "you". The difference is purely grammatical case. Thou goes where a modern sentence would put he, she or I; thee goes where it would put him, her or me.
- Thou hast forgotten. → He has forgotten.
- I have forgotten thee. → I have forgotten him.
- Thou shalt not steal. → subject
- Peace be with thee. → after a preposition, so object
The test
Swap in I/me. Say the sentence to yourself with the modern pronoun. If I sounds right, the archaic word is thou; if me sounds right, it is thee. "____ art brave" → "I am brave" → thou. "He gave it to ____" → "to me" → thee.
The verbs that go with thou
This is where most pastiche falls down. Thou takes its own verb endings, and getting them wrong is more conspicuous than the pronoun itself:
- -est on most verbs: thou walkest, thou knowest, thou goest
- irregulars: thou art (are), thou hast (have), thou dost (do), thou wilt (will), thou shalt (shall), thou wast or thou wert (were), thou canst (can)
Thee, being an object, never affects the verb: I see thee, she loves thee, they told thee.
What thou actually meant
It was not a formal word. Thou was the singular and familiar form, used to one person you knew well, to a child, to a servant, or to God; ye and you were plural and also the polite way of addressing a single superior. Using thou to the wrong person could be an insult. This is worth knowing, because modern writers often use thou to sound grand when historically it did the opposite.
One real exception
In traditional Quaker plain speech, thee came to be used as a subject as well: Thee knows what I mean. That is not an error; it is a distinct, documented usage with its own history. In every other context, keep the subject–object split.
The possessives, for completeness, are thy before a noun and thine before a vowel or standing alone: thy word, thine eyes, the fault is thine.
