Many European languages conjugate their verbs, thus:
You are | Thou art
The form of the verb changes, depending on the person. In some languages (Latin and Polish, to my knowledge), the verb form is completely different for each person, which means that the actual pronoun can be omitted. (I believe it can be reinserted for emphasis.) English can't do that. For regular verbs, only the third person singular has a distinct form. We always use pronouns (except when we don't).
However, in King Lear, at one point Lear turns to his Fool and asks him, "Art cold?" This would not be possible in current English, as the pronoun thou has all but vanished. Was it possible in actual speech in Shakespeare's time, or could it exist in the play only as a poetic flourish?