LOL, but your existence is factual because we can witness it and observe it and test your response to certain stimulus. We cannot do so with "God".
How do we know if God exists or not if we cannot taste, touch, smell, see or hear Him?
Can you taste, touch, smell, see or hear your awareness?
Many things, including radical empiricism and/or ontological naturalism, cannot be observed, tested, repeated in such a mold either. One should start by establishing one's own complete philosophy by some particular means, with all its essential components/features if one is going to insist/advocate everyone else should restrict componential validity within theirs by said means to be supposed "rational," "empirical," "scientific," or whatever. More on this below. "...[Naturalists] have no knowledge that naturalism is true since they do not have an undefeated justification for their belief. If naturalism is true, then their belief in naturalism is accidentally true."
-Quentin Smith (atheist philosopher) http://www.philoonline.org/library/smith_4_2.htm
I'm not a fan of philosophical theology. However philosophy is especially useful at moving dead horses (preferable to shooting them).
While I would be the last to question the rationality of believing in ontological non-supernaturalism as a presupposition, or as a corollary adapted because it coheres with some other accepted premise, e.g. if a given agnostic maintains evil makes belief in God improbable to them, or because God as a reality remains hidden to them, in the absence of an incontestable argument for ontological naturalism, there is no firm philosophical justification for an anti-supernaturalist to claim a supernaturalist is any more unjustified in heuristically presuming supernaturalism via Experience (speaking of e.g. the mystical ways, OBEs, etc.), or even, for the philosophical theists, e.g. abduction, than a naturalist has for operating under the premise of naturalism -although it is quite impossible to apodictically prove ontological naturalism (least of all via the canons of observability, testability, repeatability, powerful though they are for other uses once a few unprovable assumptions are employed, e.g. logic, the law of non-contradiction, and so on).
(Note: Being Orthodox I'm not so much a fan for the dicthotomies of nature/supernature, nature/grace, etc., but I'm speaking to them in philosophical terms because others have raised and/or presumed them)
Philosophy has gone down this avenue of radical empiricism (e.g. David Hume, Vienna Circle/Logical Positivism in the early 1900's); it ended in collapse, though the news will not likely reach every corner of the internet before Christ returns. Oddly enough it is frequently found as a "justification" (in quotations because it self-destructs) for non-theism, yet it is not possible to argue for naturalism on the reductionistic basis of radical empiricism either. In Hume we already saw there are no empirical data which can give us such essential commodities as universals, cause/effect (Hume showed this empirically indistinguishable from mere conjunction), other minds, etc. It does take out God, but as it happens empiricism ends up taking itself out as well, as witness the gradual devolution/destruction of the Verifiability Criterion of Meaning in the early Wittgenstein and the Logical Positivists (it is already explicit in Hume).
Take the fate of logic as an example, by which all things, including empiricism, are apprised by humans. It is patently obvious that logic cannot be explained or established "foundationally" (in the sense of outmoded classical foundationalism/verificationalism/justificationalism that is standard fare among amateur cyber-atheists) e.g. (from the thread) via the human senses of sight, taste, touch, smell, sight, or sound. For example Aristotle's Law of Non-Contradiction (something cannot be both A and Non-A at the same time and in the same sense) cannot be tasted, touched, smelled, seen, nor is it a sonic vibration.
If someone here is going to "demand" that God must be "empirically provable" (or provable in whatever manner one wishes to propose from classical to defunct verificationalist philosphy) with reference to a particular methodological prism before it is deemed admissible for other persons, like myself, who affirm God, to do so with the objectors "epistemological respect" according to some set of rational criteria of admissibility (in the sense of meeting their particular rational criteria of minimally adequate epistemological verification; let them first take the same methodological scalpel to their own selves (cf. Christ on getting the log out of one's own eye first). Let them use their own narrow criteria of "approved methods" do demonstrate that logic is reliable. Because if they are arguing methodology, or naturalism, or non-theism or whatever, they are using logic to frame such an argument. Can they establish LOGIC in order to use it using the same methods they demand others must employ to "prove God syllogistically?"Faith -tacit or explicit- in outmoded Enlightenment-style classical foundationalism simply will not do for a sound argument in the 21st cenury.
 That one cannot justify the usage of rational argument from nowhere was very humorously illustrated a long time ago in logician/mathematician Lewis Carroll’s (of Alice in Wonderland fame) highly entertaining essay "What the Tortoise Said to Achilles" (Mind 4, No. 14 (1895); (read it at http://www.ditext.com/carroll/tortoise.html
Long ago Sextus Empiricus (cf. Outlines of Pyrrhonism
) put forth the devilish argument that any justification of the value of rational proof would have to be (A) a rational proof and therefore be circular or (B) irrational and therefore of no avail in establishing the rationality of reason. Aristotle similarly argued that justificationalism would entail an infinite justificational regression (how do you finally justify something? Is it based on something which is based on something and so on infinitely?) in his Metaphysics
. Any attempt to rationally dislodge belief in reason is equally question-begging and therefore self-defeating. As it turns out at the end of the day reason cannot be (A) proven or (B) falsified. This has lead historically to two false conclusions: (C) the fideist option (“it’s all based on faith” -i.e. "faith" i the sense of a blind leap rather than the biblical sense of trust in a covenant-faithful God who reveals Himself to those who seek him wholeheartedly) and (D) the “Nietzschean” alternative of radical suspicion. The problem with option (C) is that any presupposition which is held by faith is already “meaningful” as opposed to “meaningless” before one considers whether to affirm it by faith.
For an example mentioned above in passing, Aristotle’s law of non-contradiction affirms something cannot be both A and non-A at the same time and in the same sense. The law of non-contradiction must already be operating prior to any meaningful act of presupposition or else that act of presupposition cannot be meaning-distinguished from it’s contradictory opposite. Another way of saying this is that any meaningful act of presupposition tacitly presupposes rationality norms and their justificative decisiveness. So fideism cannot “ground” reason as a presupposition without already employing it to recognize there is even such a thing as a meaningful presupposition. (D) Radical Suspicion does not work out well for similar reasons: any meaningful act of doubt/suspicion presupposes rationality norms and their justificative decisiveness to demarcate a particular doubt as meaning-distinguishable from its contradictory. Meaningful suspicion about "everything" presupposes rational reflection, else we are left with meaningless suspicions which could not be rationally recognized as suspicions.
We should also note in passing that insofar as symbolic logic is a formalized system, it is subject to the mind-boggling implications of Godel's Theorem. http://katachriston.wordpress.com/2010/12/27/godels-incompleteness-theorem-the-most-important-mathematical-theorem-in-the-twentieth-century/
The Münchhausen-Trilemma (after Baron Münchhausen, who allegedly pulled himself out of a swamp by his own hair), also called Agrippa's Trilemma (after Agrippa the Skeptic), is a philosophical term coined to stress the purported impossibility to prove any truth even in the fields of logic and mathematics. It is the name of an argument in the theory of knowledge going back to the German philosopher Hans Albert, and, more traditionally, Agrippa. Simply put, the trilemma is a breakdown of all possible proofs for a theory into three general types:
* The circular argument, in which theory and proof support each other
* The regressive argument, in which each proof requires a further proof
* The axiomatic argument, which rests on accepted precepts
The first two methods of reasoning are fundamentally weak, and because the Greek skeptics advocated deep questioning of all accepted values they refused to accept proofs of the third sort. The trilemma, then, is the decision among the three equally unsatisfying options.
Agrippa and the Greek Skeptics
The following tropes for Greek skepticism are given by Sextus Empiricus, in his Outlines of Pyrrhonism. According to Sextus, they are attributed only "to the more recent skeptics" and it is by Diogenes Laertius that we attribute them to Agrippa. The tropes are:
1. Dissent - The uncertainty of the rules of common life, and of the opinions of philosophers.
2. Progress ad infinitum - All proof requires some further proof, and so on to infinity.
3. Relation - All things are changed as their relations become changed, or, as we look upon them from different points of view.
4. Assumption - The truth asserted is merely a hypothesis.
5. Circularity - The truth asserted involves a vicious circle (see regress argument, known in scholasticism as diallelus)
According to the mode deriving from dispute, we find that undecidable dissension about the matter proposed has come about both in ordinary life and among philosophers. Because of this we are not able to choose or to rule out anything, and we end up with suspension of judgment. In the mode deriving from infinite regress, we say that what is brought forward as a source of conviction for the matter proposed itself needs another such source, which itself needs another, and so ad infinitum, so that we have no point from which to begin to establish anything, and suspension of judgment follows. In the mode deriving from relativity, as we said above, the existing object appears to be such-and-such relative to the subject judging and to the things observed together with it, but we suspend judgment on what it is like in its nature. We have the mode from hypothesis when the Dogmatists, being thrown back ad infinitum, begin from something which they do not establish but claim to assume simply and without proof in virtue of a concession. The reciprocal mode occurs when what ought to be confirmatory of the object under investigation needs to be made convincing by the object under investigation; then, being unable to take either in order to establish the other, we suspend judgment about both.
With reference to these five tropes, the first and third are a short summary of the ten original grounds of doubt which were the basis of the earlier scepticism. The three additional ones show a progress in the sceptical system, and a transition from the common objections derived from the fallibility of sense and opinion, to more abstract and metaphysical grounds of doubt.
According to Victor Brochard "the five tropes can be regarded as the most radical and most precise formulation of skepticism that has ever been given. In a sense, they are still irresistible today."
This argument runs as follows: All of the only three ("tri"-lemma) possible attempts to get a certain justification must fail:
1. All justifications in pursuit of certain knowledge have also to justify the means of their justification and doing so they have to justify anew the means of their justification. Therefore there can be no end. We are faced with the hopeless situation of 'infinite regression'.
2. One can justify with a circular argument, but this sacrifices its validity.
3. One can stop at self-evidence or common sense or fundamental principles or speaking 'ex cathedra' or at any other evidence, but in doing so the intention to install certain justification is abandoned.
An English translation of a quote from the original German text by Albert is as follows:
Here, one has a mere choice between:
1. an infinite regression, which appears because of the necessity to go ever further back, but isn’t practically feasible and doesn’t, therefore, provide a certain foundation;
2. a logical circle in the deduction, which is caused by the fact that one, in the need to found, falls back on statements which had already appeared before as requiring a foundation, and which circle does not lead to any certain foundation either; and finally:
3. a break of searching at a certain point, which indeed appears principally feasible, but would mean a random suspension of the principle of sufficient reason.
--Albert, H., Traktat über kritische Vernunft, p. 15 (Tübingen: J.C.B. Mohr, 1991).)
Albert stressed repeatedly that there is no limitation of the Münchhausen-Trilemma to deductive conclusions. The verdict concerns also inductive, causal, transcendental, and all otherwise structured justifications. They all will be in vain.
Therefore certain justification is impossible to attain. Once having given up the classical idea of certain knowledge one can stop the process of justification where one wants to stop, presupposed one is ready to start critical thinking at this point always anew if necessary.
This trilemma rounds off the classical problem of justification in the theory of knowledge.
The failure of proving exactly any truth as expressed by the Münchhausen-Trilemma does not have to lead to dismissal of objectivity, as with relativism. One example of an alternative is the fallibilism of Karl Popper and Hans Albert, accepting that certainty is impossible, but that it's best to get as close as we can to truth, while remembering our uncertainty.
Fig. Escher's Dragon