Okey-dokey then, here goes....
The naturalist argues that all that can be said to exist is matter, energy or that which can be percieved logically as deriving from matter or energy.
Nathan added something important along the lines of valid knowledge can only come from direct observation and experience and the logical inferences that the mind can draw from such things by using reason or rational thought.
Now here's the problem as I see it.
Matter and energy came about we know not how. That in itself is problematic but it's not the point of my post at the moment; which is to argue against naturalism as per the definition. One thing I am pretty certain of, however, is that no naturalist thinks it came about as the result of an eternal Mind or Reason.
Let's say it came about by accident. This is a rather inexact phrase, but all I mean by accident is that it was not caused by a rational being. If you can think of a better word than "accident" then please jump in.
So ... mindless matter and energy just goes about its business in accordance with the similarly uncreated and mindless laws of physics, chemmistry, probability etc.
By a very, very (but not impossibly) slim chance the environement in one part of the vast universe brings about a complex and self-replicating molecule. All by chance. No rational, planning mind behind it.
The laws of physics, biochemistry, natural selection etc bring about adaptations to these moleculels and we have something recognisable as "life". Chance mutations allow selection pressure to act and life evolves.
One product of this evolutionary process is a very odd animal indeed (I nearly said "creature" there, but it was not created).
This presumptuous little animal experiences its surroundings through a very highly developed series of pathways. It is bombarded with experiences and observations. It is presumptuous, however, because it attempts to make sense of these observations and experiences via what it calls logical and rational inferences. It claims that such inferences are valid and some of the more presumptuous human animals actually claim that some things are true and untrue.
Matter and energy and the laws of physics etc have no reasoning power and yet this human animal thinks it does. It thinks it can make inferences about how reality actually "is" or even might be, when in "reality" what is happening is that matter and energy are simply providing a subjective phenomenon we call consciousness. No reasoning is actually objectively valid. No truth can be perceived. What we experience when we are reasoning like everything else is simply the outworkings of mindless matter and energy at one point in its existence.
One such inference from observation and experience is that all that exists is matter or energy or that which can be derived from such. Such a reasoning is as merely subjective as all the rest.
Naturalism invalidates naturalism.
It is an argument that refutes itself.
As such, whatever is "true" about the universe; then it certainly is NOT naturalism as this is the negation of any truth or any reasoning or any inference being anything more than a completely subjective phenomenon.