Descartes is a great Christian philosopher and I am a guy who reads him yearly and hopes to understand. Being critical of Descartes should only be done with care, but I do have a complaint. This world-class scientist and thinker failed, I think, and the failure keeps coming up in conversations with friends and readers. If I am reading him correctly, he wanted to build his system of thought on certainty and this quest for certainty has led to three very bad results in this particular culture.
Few people accept his conclusions, a secure Christian theism based on his arguments, but plenty are infected with his desire for certainty. This is a snare and a delusion that would rob us of a chance to find maturity: wondering brings us to maturity.
We cannot wonder about certainty.
First, I meet Christians who agree with Descartes, but because they are not certain about religious ideas, they simply give up on reason. If the test of reason is being sure, then almost nothing meets the test. As a result, Christians pervert our reasonable faith into a jump into irrationality. The result has been bad. In some of the Christian Left, this type of “faith” (really existentialism) centers around feelings of kindness and community. Truth takes second place to “feels.” In a part of the Christian Right, there are certain doctrines, ideas, or practices that no longer need to be scrutinized. We simply assert them, hard, and anyone who disagrees is out.
God save us from both approaches.
Second, more rarely I bump into Christian apologists who fantasize they have improved on Descartes and do have arguments that are certain. Everyone reasonable must be a theist, Christian, and even their brand of Christian! Failure to agree is simply mental perversity! This is wrong, hopelessly wrong.
Christianity is reasonable, but there is always a gap between what we think and reality. We are not sure about much of anything that matters. This is where faith is necessary: agreement with ideas based on reason and evidence, but without certainty. One always is doing the best one can!
Third, one finds non-Christians, atheists and other non-theists who think science is certain so it meets Descartes’ test. Everything other than science is nonsense. They might agree in principle that any theory in science is provisional, but cannot really name an idea in current science they predict will fail. They forget what the late WV Quine demonstrated: every idea in science is underdetermined by the evidence.
Every statement in science is a maybe and there is no certainty to be found. Metaphysics and physics are alike in this way, though the type of evidence is different. Maybe. Science itself is a system based on mathematical ideas, not a part of science, and decent, reasonable metaphysical assumptions. Science can never choose between such basic metaphysical ideas as idealism and materialism. Are we basically an idea in the mind of God or matter and energy in mindless motion? Scientists may assume one or the other, but science cannot conclusively answer the question. It can nudge us in one direction or the other, but we will never be sure.
Descartes, if successful, would have left no room for faith: the maybe based on evidence and best experience in constant dialog with changing evidence.