There is an intriguing philosophical phenomenon which has arisen within the last few centuries: the belief that when human beings (but especially theists) attempt to reason apart from sense experience, that cannot itself provide us with factual knowledge.
To illustrate such commitments, allow me to illustrate two claims made by David Smalley in his book The Baptized Atheist:
An Atheist rejects all super-natural existence and prefers to live by empiricism, the theory that knowledge can be acquired only through direct observation and experimentation rather than through metaphysics and theology.1
This makes sense on the surface of things, considering David's presuppositional commitment to naturalism, which includes the idea that no gods exist, or that if any of them do exist, he has not personally come to know them through empirical observation or testing. After all, given his admittedly limited investigation into such topics, David is aware that metaphysical statements are about some kind of "supra-sensible" reality which is not directly experienced or verified by "natural" science. But that isn't the only claim which David makes in his book about the limits of knowledge and facts. He continues elsewhere, after a few more pages of illustrations about Christian beliefs that appear to be circular, insisting that:
As I present evidence contrary to any of the above circular reasoning statements, the confirmatory bias of theists has them searching for answers of validity in the very book I am asking them to validate. Simply put, you cannot convert an Atheist to Christianity by citing the very doctrine he or she rejects. Proof must come from outside sources and be logical, reasonable, convincing, and obtained through empiricism. No religious doctrine in history has been proven as absolute; therefore none of them fit that description.2
If I am understanding David correctly, he believes that all informative or factual statements about the objective world must be derived empirically (based on experience, observation, sensation), and therefore, in order for any human being to "obtain" justified true knowledge (i.e. proof), such knowledge cannot transcend particular, physical experience or the appearance of the senses. And because metaphysical claims are not able to be brought to the critical test of sense experience, they are concluded to be illogical, unreasonable, and unconvincing (i.e. nonsense, or senseless).
This, as I see it, is an excellent example of how offensive the field of metaphysics is to the common intellectual outlooks of modern atheism. Metaphysics presumes to tell us something about the objective world which we don't directly know in ordinary experience, and which can't be verified through the methods of "natural" science. Skeptics of theism (and often, Christianity in particular) view metaphysical reasoning as conflicting with empirical science as the one and only way to acquire knowledge.
All of this, as I have said before, is perfectly reasonable given atheistic pre-commitments to the nature of reality as a whole. But I would like to point out a few important details about David's claims, and thereby the claims of any other who, like him, "prefers to live by empiricism, the theory that knowledge can be acquired only through direct observation and experimentation rather than through metaphysics and theology."
The first detail I want to point out is that such a claim about the limits of knowledge is itself a metaphysical claim. How can David know for certain that "knowledge can be acquired only through direct observation and experimentation..."? Such a dogmatic statement is not found in the objective world of sense experience, and is itself not known as the result of empirical testing and experience. Has David ever sensed that statement in the real world? It is a non-material, mental construct. Has David ever tested or observed all knowledge? Has he even tested or observed all the tests about what has been observed, and thereby known? Indeed, if it were actually true that knowledge can only be acquired through direct observation and experimentation, then--on the basis of David's own anti-metaphysical claim--no one else in the world could ever know that it were objectively true, because that statement is itself not known as the result of empirical testing and experience. It turns out that claims like David's reflect the subjective (and sometimes arrogant) bias of the one pronouncing it.
The second detail I want to point out is in the form of a question: What rational basis, or what rational evidence is there for David's commitment that all knowledge must be empirical in nature (i.e. only through direct observation and experimentation)? I find it ironic that such a dogmatic statement precludes any other type of verification or support other than empirical warrants or evidence. Such an assertion is not a conclusion supported by other reasoning. And the premise3 does not admit of empirical verification since it deals with what is universally or necessarily the case (i.e. not a historical or contingent truth). So it turns out that David holds to his dogmatic conclusion4 in a presuppositional fashion, as something which controls all inquiry, rather than being the result of inquiry. By the way, I think that's fair for him to believe. But I also think it appears capricious for all those like him with anti-metaphysical leanings to prohibit the theist from doing what is allowed for him!
That brings me to my third and final point. When David insists upon the acquiring of knowledge only through empiricism "rather than through metaphysics", that is an admittedly theoretical truth claim. And if that theoretical claim is itself true, then the uniformity of nature cannot be known to be true, in which case the whole enterprise of "natural" science would immediately be undermined. Stop and think about it for a minute. If all knowledge must be empirical in nature, then the uniformity of nature cannot be known to be true. And without the knowledge and assurance that the future will be like the past (e.g. if sugar dissolved in a cup of water today, it will continue to do and not explode in a cup of water tomorrow and the next day, and even next year) we could not draw empirical generalizations and projections at all. Scientists could not arrive at even one dependable, rationally warranted conclusion about future chemical interactions, or anything else. Pick anything: the rotation of the earth, the stability of the chair you're sitting on, or the effects of a pharmaceutical drug. Each and every premise that entered into the scientists reasoning about a particular situation at a particular time and in a particular place would need to be individually confirmed in an empirical fashion. Nothing experienced in the past could become a basis for expectations about how things might happen at present or in the future. Without certain beliefs about the nature of reality and history--beliefs which are supra-empirical and meta-physical in character--the process of empirical learning and reasoning would become impossible.
Please, please, please learn what the study of metaphysics is before buying into such strange dogmatic claims like "knowledge can be acquired only through direct observation and experimentation rather than through metaphysics." Metaphysics studies such questions or issues as the nature of existence, the sorts of things that exist, the classes of existent things, limits of possibility, the ultimate scheme of things, reality versus appearance, and the comprehensive conceptual framework used to make sense of the world as a whole, and not merely in its parts.
1. Smalley, David. Baptized Atheist (Kindle Locations 1914-1917). American Atheist Press. Kindle Edition. Emphasis in bold and italics is mine.
2. Ibid. Emphasis is mine, again.
3. That there cannot be a non-empirical source of knowledge or information about reality
4. That it's illegitimate to draw inferences from what is experienced by the senses to what must lie outside of experience--like the existence of supra-natural beings.