This paper examines the attempt to eradicate vagueness, as understood as a specific philosophical idea concerning borderlines, from UK educational assessment in a misconceived attempt to establish reliability as the key component of competent high stakes assessment. The issue is not one restricted to the UK in that wherever competence is understood to be something that is necessarily reliable (in the sense of consistent), the issues examined here arise. The erosion has diminished the scope of what is taken seriously in educational culture and potentially damaged the competitive edge of any system that does this. In the context of increasing globalisation this is not a trivial issue. The paper sets out what vagueness is, how the UK assessment system deals with the issue of reliability and consistency at the moment and how the re-introduction of vagueness in our assessment system will bring about positive change for both our teachers and students by raising standards of education and broadening the range of what education takes seriously.