The Instability of Vague Terms

Timothy Williamson's response to the question why we cannot know where the sharp boundaries marked by vague terms lie involves the claim that vague terms are unstable. Several theorists would not accept this claim, and it is tempting to think that this gives them a good objection to Williamson. By clarifying the structure of Williamson's response to the title question, I show that this objection is wrong-headed, and reveal a new line of attack.