The first flaw is in their presupposition that their deity Yahweh or Jehova exists. This presupposition is just that. It is not based on facts or objective and empirical evidence. The first problem that needs to be addressed is where does this presupposition come from? The most obvious answer is that we were taught that there is a supreme deity that exists by either friends, family, or society in general. Here in the U.S. Christianity is the dominant religious institution and belief system in the entire country. We have 'In God we trust' imprinted in our currency and even inscribed in our court rooms. Many of our traditional ceremonies are imbued with Christian ideals such as weddings and funerals.
When I come across believers who wish to debate me on the issues related to their beliefs, I usually ask a series of questions in hopes of helping them see their erroneous line of reasoning. When asked for instance "Where do you think that you came from?" I usually reply with a very honest; I don't know how life began or how the universe came to be. Science knows that there was a big bang and that most likely we arose from a combination of the various chemicals present in the early earth combined with the right environmental conditions, but we don't know how the actual process took place. In the end it seems more plausible than to assume that an invisible, indescribable, unknown deity was responsible for it all.
When I ask believers how they know that their god exists I usually get the standard replies based entirely on subjective evidence. They feel him when they pray. they hear his voice or sense his will for their lives in their hearts, or they are blessed with the gift of the Holy Spirit. What they don't realize is that all of these apparent phenomenon could be easily explained through psychology, psychiatry, and other disciplines relative to how the mind works and how we interpret our experiences. What Christians need to realize is that subjective evidence is not evidence at all when it comes to proving that a god exists. If that were the case then everyone claiming to have experienced god in other religions must also be believed and their subjective experiences should be considered just as credible. Of course if we were to do that then we would have another problem: which god is the true god and how can we know that?
a : the study of evidences of design in natureb : a doctrine (as in vitalism) that ends are immanent in naturec : a doctrine explaining phenomena by final causes
Based on the definition above all Christians are teleologists; that is, they base their beliefs on all the apparent design that they see in nature. The doctrines of creationism or intelligent design are both based entirely on this assumption. God did it is the mantra of all creationists and ID proponents and they base their beliefs entirely on the god of the gaps theory. Basically what they do is attack science by picking on specific areas in which our knowledge is not yet complete. Abiogenesis is a popular target for creationists since it addresses our lack of knowledge regarding how life came about from inanimate matter. Science is still unclear about the actual process of how life came about but what we do know is certainly more plausible than God did it.
Next, I have to ask them about how they know that the Bible is the word of God. I often get some interesting answers. The most common one and in my opinion the most ignorant one is that it was written by men inspired by God. But that only leads me to ask them how do they know this? The only answer is that the bible says this within its pages.
All Scripture is God-breathed and is useful for teaching, rebuking, correcting and training in righteousness, 2 Timothy 3:16
For prophecy never had its origin in the human will, but prophets, though human, spoke from God as they were carried along by the Holy Spirit. 2 Peter 1:21
Although many atheists are familiar with the Bible and have actually read it, the problem generally lies in that we don't believe in your god, nor that he inspired a book or revealed himself and his will to man through that book. The Tanach, New Testament, the Koran, the Bhagavad Gita and all other so called divine texts are viewed by most atheists as nothing more than the products of men. To accept any of them as the word of gods would be to beg the question, because there is no evidence that any of these gods exist outside of the imaginations of men.
The bottom line is that when it comes to Christian claims, the Bible is not evidence of the existence of your God. Subjective experiences such as visions, dreams, or the experience of the Holy Spirit are also not considered evidence. In order to prove that your God exists you must take on a monumental task. You must be able to prove that he exists both objectively and empirically which to date is impossible due to the hiddeness of god. Also, if you were to prove that your god exists then you must identify this god as the one you profess to believe in.
The Bible makes it clear that you cannot know God unless you make a commitment based on faith that he exists. Basically you are stating by doing so that "I have not seen nor heard God speak but I know that he is." Faith in layman terms is nothing more than an assumption based on a commitment to belief without evidence.
assumption: something that is believed to be true or probably true but that is not known to be true : something that is assumed
The entire Christian faith as well as others are based entirely on bad assumptions. The assumption that God exists, that his name is Yahweh or Jehovah, that he is eternal, that he exists outside of space and time, that the Bible in this case is his inspired word, and that he is the creator and first cause of all things that began to exist. In this case I dare to conclude that absence of evidence is evidence of absence.
Note: All biblical citations are taken from the NIV of the scriptures. Word definitions are taken from the Merriam Webster dictionary online.