When is a belief rational?

Skeptics of Christianity (e.g. atheists, agnostics) often assume that there is something epistemically sub-par about Christian belief. In many cases the thought is that Christian belief is somehow unjustified or irrational. Indeed, the more uncharitable and undisciplined will even take to calling Christians such incendiary epithets as "insane" or "crazy". But all this begs the question: what is the theory of rationality being assumed here?

Rather than probe the skeptic's mind, let's focus on an appropriate definition of rationality. In this regard philosopher Anthony Kenny nailed it when he defined rationality as the mean (that is, the optimal balance) between skepticism and credulity. That is, you doubt when doubt is appropriate and you believe when belief is appropriate.

This is important because too often rationality has been associated solely with skepticism. For instance, the rational person is the skeptic who doubts everything until he/she can corroborate it independently.

This deeply skewed understanding of rationality owes much to Descartes, the seventeenth century Catholic philosopher who advocated a method of doubt on which certain knowledge could be based. But it owes much as well to a particular understanding of science as rooted in the falsification of hypotheses. If a truly scientific hypothesis is one that could be falsified, then it is one that is open to doubt, and thus there is a heavy emphasis on skepticism.

The fact is however that nobody who is considered rational lives purely in accord with the skeptical dimension of rationality. Even the most skeptical scientist believes the testimony of peer-reviewed research in Scientific American as well as the directions he gets from a passerby.

Here is the dilemma: the person who is highly skeptical of only one subset of beliefs (e.g. the religious) appears arbitrary. But the person who is highly skeptical of all beliefs appears insane.

Once we recognize that belief is an essential part of rationality, we will be well on our way to a correct appraisal of the epistemic status of Christian belief.