It's basically the remnant of Germanic influence on English. In German, the second person takes -st, e.g., "Ich bin, du bist, Ich kenne, du kennst" (I am, you are, I know, you know).

The old English forms follow the same pattern, as Kosmonaut shows above. This is the easiest way to spot "fake Elizabethan" language in books and movies. "Wouldst thou?" is fine, "wouldst I?" don't fly.

It's basically a feature of being a Germanic language. In German, the second person takes -st, e.g., "Ich bin, du bist, Ich kenne, du kennst" (I am, you are, I know, you know).

The old English forms follow the same pattern, as Kosmonaut shows above. This is the easiest way to spot "fake Elizabethan" language in books and movies. "Wouldst thou?" is fine, "wouldst I?" don't fly.