Some friends and I recently engaged in a long conversation regarding what kind of reasons would be sufficient for any of us, personally, to believe God does or does not exist. We began with the question of whether or not people ever have reasons for believing in something, whether that something be the existence of God or the existence of the hand with which I'm typing this response. We concluded that people believe for a variety of reasons, some emotional, some experiential, some rational, etc. We also determined that only a small category of reasons constitute evidence, as in the kind of evidence that would be acceptable in a court of law or a laboratory study. We argued that no evidence could be found for the existence of God, and furthermore, although certain kinds of reasons are sufficient for others to believe in God, with the exception of one, these same reasons were not sufficient to us, personally.
None of us considered the great works of world religions to constitute a reason for us to believe in the existence of God. Our grounds for such a conclusion are, roughly, as follows. Imagine, as some people have, that every story told in a great religious text is historically true. In other words, Jesus, Rama, Buddha, Muhammad, or some other figure spent time upon this earth and carried out the deeds the great works claim they carried out. Does this mean God exists? We concluded that no, a historical account of an individual who lived, who performed miracles and who made claims regarding the existence of God no more constitutes evidence for the existence of God than, say, an individual alive today who performs amazing feats and claims that God exists. Why? There is nothing inherent in a so-called "miracle" that necessitates the existence of God, anymore than there is anything inherent in a highly-charismatic religious leader that necessitates the existence of God. Although we would certainly have an interesting question on our hands---how does this person perform said miracles?---our hypotheses may point in many directions: magic, not yet understood science, God, demons, aliens, delusion, trickery, etc. Thus, we could not believe in the existence of God based on the words and deeds of historical figures in the great religious works of humanity.
We also did not consider the argument from design---in any of its guises---to constitute a reason for us to believe in the existence of God. Our understanding of the laws of physics, of early galaxy formation, of evolution, and of other natural laws and processes strongly suggest to us that these alone are sufficient to account for the amazing and elegant complexity of the universe. Although we recognize that there are those who argue that these natural laws and processes must surely have themselves been created, we place them in roughly the same category, in terms of origins, as God. In other words, just as religious individuals argue that the complexity and elegance of the universe owes its existence to a God whose origins cannot be accounted for, so we argue that this same complexity and elegance of the universe owes its existence to natural laws and processes, the origins of which cannot (yet) be accounted for. If God---despite the amazing elegance and complexity of such an entity---need not be explained as a creation of some preexisting "Mover", neither do the natural laws and processes need to be explained as creations of God. We find this explanation especially superior to the argument that "God did it" because natural laws and processes are observable and demonstrable, whereas God or gods are not observable or demonstrable. It makes more sense, then, for us to argue that these natural laws and processes are responsible for "the way things are" than God. Thus, we could not believe in the existence of God based on any sort of argument from design.
Three of the four of us agreed that we could believe in the existence of God or gods on the basis of a compelling experience of God---a hierophany or theophany, depending on what kind of "God" we're looking at. Those of us who agreed that such an experience of contact or communion with God would be sufficient evidence for us to believe in God, provided that experience was powerful and compelling to us personally. We agreed, furthermore, than should one among us have a vision or other experience of God, their experience would not constitute a reason for the rest of us to believe; in other words, such an experience would be a personal reason for believing, but would not be compelling to others. Just as we cannot believe in God on the grounds of the words and deeds of men or women in religious texts, so too can we not believe in God on the basis of our friends' personal convictions and experiences. We would have to have those experiences ourselves in order to believe. The one friend who disagreed with this stance argued, furthermore, that no experience of God he could possibly have would be compelling to him; he would always, he argued, explain such an experience away as a dream, delusion, hallucination, wishful thinking, or other, ontologically different experience than an experience of God. Although the rest of us argued that he could not make a claim like that without first having had such an experience, he could not be persuaded.
Thus, the only reason any of us would believe in God was if we had a compelling personal experience of some kind wherein we strongly felt we had encountered God.
