Generally speaking, Naturalism is a philosophical system which holds that everything can be explained by means of natural causes. Naturalism can be summed up with Carl Sagan's infamous quote that "The Cosmos is all that is,
or ever was, or ever will be."
 Naturalism denies the existence of the supernatural and is thus opposed to supernaturalism. It is held by virtually all atheists. Modern day proponents of naturalism include Richard
Carrier, Keith Parsons, and Michael Martin.
In C. S. Lewis's book
Miracles: A Preliminary Study, he accuses naturalism as being self-defeating because it undercuts the basis for rational thinking. However his argument was disputed in 1948 by the Catholic philosopher G. E. M. Anscombe. Lewis subsequently revised
his argument in the 1960 version of Miracles. Since then, there have been other individuals who have defended Lewis's argument against naturalism. Victor Reppert has defended and reformulated Lewis's argument in his book
C. S. Lewis's Dangerous Idea: In Defense of the Argument from Reason.
Alvin Plantinga has also criticized naturalism in his books Warrant and Proper Function and Warranted Christian Belief. He presents what he calls an evolutionary argument against naturalism. Plantinga argues
that the probability that our cognitive faculties are reliable given naturalistic evolution is low, and as such we have an defeater for naturalism.
- C. S. Lewis, Miracles: A Preliminary Study
- Victor Reppert,
C. S. Lewis Dangerous Idea: In Defense of the Argument from Reason (IVP, 2003)
- Alvin Plantinga, Warrant: The Current Debate (Oxford University Press, 1993)
- Alvin Plantinga, Warranted Christian Belief (Oxford University Press, 2000)