Who did Ambedkar say the Shudras were, and how are they different from Untouchables?
He wrote a whole book on the question in 1946, partly to correct a confusion that is still common: the Shudras and the Untouchables are not the same. In the classical fourfold order — priest, warrior, merchant, servant — the Shudra is the fourth and lowest rank, but he is inside the system. The Untouchables are not a fifth rank; they are outside and below the four altogether, which is what untouchability means. Lumping them together erases the very line that defined Ambedkar's own people.
His historical thesis about the Shudras was deliberately provocative. He argued that they were not a servile class from the beginning but had once been a ruling people, degraded to the bottom of the order after a conflict with the priestly class. Like his account of the origin of untouchability, this was a reconstruction meant to unsettle the idea that the hierarchy was natural or eternal — to show it as the outcome of a struggle, and therefore as something that could be undone.