There are a few theological ideas floating around out there that have become quite popular principally because they appear to provide quick and easy answers to difficult and complex problems. Some of these ideas are not particularly widespread, but have become fundamental matters of faith in certain quarters, for example, the notion of Biblical literalism. This idea had its germ in the rather more sensible notion of Biblical inerrancy, but it was taken to a ludicrous extreme. Although not many Christians subscribe to the idea, some of those who do subscribe to it are big enough loudmouths that they make the rest of us look foolish in the eyes of some.
Other ideas of this kind are not so poorly founded and are more widespread, but equally problematic. As I ponder these ideas it occurs to me that one of the elements in their success, at least in certain quarters, is precisely their simplicity. Perhaps this reflects something like a theological analogue to the principle of parsimony: any account that does the same explanatory work as some other account is to be preferred if and only if it is less complex in its structure. In some quarters parsimony is called the principle of simplicity, or sometimes Occam's Razor, after the 14th century English philosopher William of Ockham, whose famous slogan "entia non sunt multiplicanda praeter necessitatem" amounts to a kind of proto-parsimony.
But there is simplicity and then there is simplicity. On the one hand, parsimony can be very useful in keeping things clear. Consider a mathematical proof. If you can derive a theorem in just a dozen steps using only the most transparent axioms and rules of inference, then why appeal to another proof that justifies precisely the same theorem but that requires hundreds of steps and appeals to obscure hypotheses and controversial rules of inference? From an explanatory point of view, it just doesn't make any sense. On the other hand, consider two explanations for the existence of life here on the earth. Assume that both explanations appeal directly to the Neodarwinian synthesis of evolutionary biology and molecular genetics, but one theory, A, leaves it at that, while the other theory, B, includes the axiom "And God created the world in just such a way that these forces of natural selection have these effects on these sorts of molecules". Clearly Occam's razor will have us preferring theory A over theory B, since both theories do precisely the same explanatory work, but theory B adds an entity, namely God, that is lacking in theory A, and nothing about the theories themselves suggest that this particular entity has anything to do with the explanation at hand.
From an empiricist standpoint, that is. If one is not an empiricist, then one can have independent reasons for favoring theory B over theory A without violating parsimony. But it is important to note that parsimony is, in itself, not a requirement of an explanation. The mathematical proof of hundreds of steps is just as valid as the proof of a dozen steps--the only difference is that one is simpler than the other. Only if we want the proof to be perspicuous to the average mind need we prefer the simpler proof over the more complex proof, provided that the two proofs really accomplish precisely the same thing, that is, proof of the theorem in question.
Suppose, however, we return to theories A and B and ask the question: what if the entity added in theory B, God, is not, in fact, praeter necessitatem? This is a centrally important question because the existence of God is not one of the proper objects of the empirical sciences. The principle of parsimony is quite useful if what one wants to do is to show, for example, that phlogiston is not needed in our account of combustion, but parsimony alone cannot tell us that an entity such as God is not needed in any explanation of the origins of life. To merely assert that God is not "needed" is to adopt an a priori metaphysical commitment that is not rationally warranted, though it is commonly enough done. In short, nothing about the principles of explanation in themselves can rationally warrant the exclusion of God from an explanation without begging the question.
I mention all of this as merely prefatory to some remarks I would like to make regarding two theological principles that I think are often defended by their adherents with similarly question-begging arguments. The two principles that I have in mind are Sola Scriptura and Sola Fides, and I will discuss them in a subsequent post. Each is widely held in certain Protestant quarters (though not necessarily in all, nor are both held equally by all) and each has been used as a matter of complaint against Roman Catholic theology amounting, for some, to a reason not to become Catholic. This aspect of the problem is given an excellent analysis by Fr. Al Kimel of Pontifications in this post, and discussion of that analysis is now open at Dr. Mike Liccione's blog, Sacramentum Vitae, here. What I will focus on in my own treatment will be the nature of the arguments used to defend these principles. I will show that neither principle is rationally warranted as a reason not to be Catholic in precisely the same way that appealing to the principle of parsimony to exclude God from any and all explanations is question-begging. As I mentioned at the outset, I think that part of the appeal of these principles lies in the fact that they are widely perceived as doing a lot of explanatory work in just a few simple and perspicuous steps, and folks are always looking for the magic bullet that will kill off all the explanatory demons in one fell stroke. These principles, however, will not do the trick.