<P> The British philosopher Simon Blackburn has criticized this formulation by suggesting that we do not want to accept as knowledge beliefs, which, while they "track the truth" (as Nozick's account requires), are not held for appropriate reasons . He says that "we do not want to award the title of knowing something to someone who is only meeting the conditions through a defect, flaw, or failure, compared with someone else who is not meeting the conditions ." In addition to this, externalist accounts of knowledge, such as Nozick's, are often forced to reject closure in cases where it is intuitively valid . </P> <P> Timothy Williamson has advanced a theory of knowledge according to which knowledge is not justified true belief plus some extra condition (s), but primary . In his book Knowledge and its Limits, Williamson argues that the concept of knowledge cannot be broken down into a set of other concepts through analysis--instead, it is sui generis . Thus, according to Williamson, justification, truth, and belief are necessary but not sufficient for knowledge . </P> <P> Alvin Goldman writes in his "Causal Theory of Knowing" that knowledge requires a causal link between the truth of a proposition and the belief in that proposition . </P> <P> A central debate about the nature of justification is a debate between epistemological externalists on the one hand, and epistemological internalists on the other . </P>

The root means the study of or branch of knowledge about