A philosophical problem that presents three possible ways we could justify beliefs that constitute knowledge: (a) circular reasoning (beliefs must justify one another), (b) regressive (beliefs must all be justified by other arguments on and on forever) or (c) axiomatic (some beliefs are self-evident). It is often thought that knowledge consists of justified true beliefs (that must be justified by an argument or axiom). The problem is that all three of the possible ways to justify beliefs that constitute knowledge seem to have problems. Circular arguments are fallacious, regressive reasoning can never be completed by people (who are finite beings), and what we think of as axioms can always be questioned and are often proven to be false at some point.