Full Idea
Reasoning, it seems, can only justify us in holding a belief if we are already justified in holding the beliefs from which we reason, so reasoning cannot provide an ultimate source of justification.
Gist of Idea
Reason cannot be an ultimate foundation, because rational justification requires prior beliefs
Source
J Pollock / J Cruz (Contemporary theories of Knowledge (2nd) [1999], §2.1)
Book Reference
Pollock,J.L./Cruz,J: 'Contemporary Theories of Knowledge (2nd)' [Rowman and Littlefield 1999], p.29
A Reaction
This sounds slick and conclusive, but it isn't. If we accept that some truths might be 'self-evident' to reason, they could stand independently. And a large body of rational beliefs might be mutually self-supporting, as in the coherence theory of truth.