While I'm a huge fan of Reason and the Enlightenment, Descartes and Hume and other rationalists of their day seemed to have had a relatively naive view of Reason. It would be interesting to read something on the history of the development of Philosophy's perception of Reason from the Pre-Socratics to Post-Modernism/Structuralism (which I'm not a fan of).

As a fan of Quine, Wittgenstein et al, how can anyone say "the ratio of circumference to diameter is equal to pi"? Granted, "pi" can be "defined" as such, but its value (3.14...) can only be derived empirically (by measuring). It seems like once empirical truths are embedded deeply enough, they they appear in the mind as (i.e., become) truths of reason (I blame Plato for this).

That said, I think "self-evident" is entirely appropriate (e.g., "all men are created equal in a Kantian sense) from a pragmatic perspective.