. . . like existential inferences in experimental physics, in historical research, and in judicial proceedings, existential inferences in theology fall short of achieving the certitude attainable in mathematical demonstrations or proofs. If we are able to show that we have reasonable grounds for believing in God’s existence, that belief will have for us a degree of probable truth, somewhat akin to what to what is described as being “beyond a reasonable doubt” or as resulting from a “preponderance of the evidence.”
Two characteristics of all other existential propositions also characterize the proposition “God exists,” and have a bearing on attempts to argue for the truth of that proposition. No existential proposition can be self-evidently true or necessarily true. When we have direct perceptual acquaintance with a particular individual, the existence of that individual is evident to us, but the proposition which asserts that the individual exists is not self-evident, nor is its truth necessary. Self-evident propositions are propositions which we know to be true directly from our understanding of their component terms, not by process of reasoning or inference.
Mortimer Adler, How To Think About God (Touchstone: 1980) p. 104