The Renaissance philosophers took for granted the existence of a God. To Pico and Montaigne the existence of a God was a foregone conclusion and was the foundation of their philosophies. The modern philosophers Sartre and Carnap dispute any belief in God and one of them bases his philosophy on the nonexistence of a God.
Jean Paul Sartre, in his treatise on existentialism, stated that there is no God. Indeed, the absence of a God is essential to existentialism. According to Sartre, if there is a God, then man is conceptualized in the mind of that God according to some divine blueprint, and man's essence (the formulae and the qualities which define man) precedes his existence much the same way that a paper cutter's essence (the concept of its function and its physical design) precedes its manufacture. If there is even a basic human nature, in the absence of a God, which determines that each man is a particular example of a universal conception, then man's essence still precedes his existence. But, according to Sartre's existentialism, there is no God; there is no human nature: man's essence does not precede his existence. A man is first born into existence. Then, and only after his existence is established, he creates his own essence through deeds and accomplishments. Those deeds and accomplishments are, in turn, the result of choices born out of absolutely free will. There is no God to tell him which is the best or the worst choice. A man's choices are his and his alone.
Now God, as understood by the Renaissance philosophers and by Sartre, is some undefinable, etherial entity that exists (or does not exist) outside the realm of what man understands as the physical world. God isn't something one can see, touch, or hear. God must be accepted on faith alone. In this regard, Rudolph Carnap, while he did not actually discuss God in those of his writings that I read, would say that the existence (or the nonexistence) of a God is neither directly nor indirectly verifiable. He would say, "No God has come to me and shown me unequivocal proof that He is a God and that He exists, and no one has come to me and shown me any tangible evidence that a God cannot exist. Likewise, there is no indirect proof that God either does or does not exist. Using the iron key as an example, I have not seen a key made of iron (verified by all known empirical means except by magnetic properties) that has had its magnetic properties removed. Such a feat is outside the capabilities of mankind and, therefore, could be accomplished only by a God (such evidence, while not proof positive, would lend credence to the existence of a God)." Carnap would then say, "The concept of God belongs in the realm of metaphysics. Any propositions that a God exists (or does not exist) have no empirical sense. There is no empirical data relating to a God that can be observed or measured directly or indirectly, so any propositions relating to the existence, (or the nonexistence) of a God are moot."
Carnap would carry this further and state that there is no sense to existentialism because existentialism depends on the absence of God and, therefore, any propositions relating to existentialism cannot be valid because the nonexistence (or the existence) of a God is not empirically verifiable, and hence the concept of existentialism is as moot as is the concept of God.
I have stated that the concept of God, as modern man understands it, is of some intangible, etherial entity that exists outside the physical realm. There is another possibility.
Zecharia Sitchin is a scholar who has made the study of ancient texts his life's work. His interest in them began in his early youth when he became intrigued with the book of Genesis. Since then, he has studied writings from Sumer, Akkad, Babylon, Assyria, Mesopotamia, Egypt, Greece, Rome, and more. He studied the languages these texts were written in and translated them for himself. His translations are not completely mainstream. For example "...in my name..." as translated by Sitchin would be "...in my vehicle...". Taken in context, his translations do not belie the the sense of the sentence from which they are taken, nor do they belie a better than even probability that they might be correct.
Sitchin, in his six-book Earth Chronicles series, stated that there is a tenth planet in our solar system (it is about four times the size of Earth) called Nibiru by the Sumerians (the Babylonians called it Marduk) whose orbit describes and extremely elongated ellipse and whose period is 3600 years. Thus, it remains unseen from Earth for long periods of time. The next time it will be seen from Earth is around 3400 AD.
Sitchin makes two other assertions that are of prime significance: Nibiru is inhabited (he refers to the inhabitants as Anunnaki), and its atmosphere is undergoing some form of erosion that can be corrected only by somehow suspending gold within it.
So it was that the first Anunnaki came to Earth 445,000 years ago in search of the element that would save their planet. Thier leader was a scientist-engineer named EN.KI. He set about to extract gold from the waters of the Persian Gulf around the base camp he established at Eridu (in what is now southern Iraq). When the supply was nearing exhaustion, EN.KI found a huge supply of gold in Africa and the Anunnaki began mining operations there.
After a time, the Anunnaki became enraged at the terrible conditions in the mines and revolted (this occurred some 300,000 years ago). ANU, king of the Anunnaki and father of EN.KI, was sent for and he mediated. He questioned what could be done to solve the problem. EN.KI proposed a solution and ANU agreed.
The soultion was genetic engineering. EN.KI would create a new species: a cross between the Anunnaki (for intelligence) and the anthropoids who inhabited the Earth at that time (for physical strength and stamina). At first they were sterile (as are mules which are a cross between horses and donkeys), but with some additional genetic manipulation, the new species was given the capability of reproduction. And thus it was that man first inhabited the Earth.
As I said, Sitchen referred to the visitors to Earth as Anunnaki, but man referred to them as gods - not Gods as in supernatural beings, at least not in the beginning, but gods as in a hierarchical structure of speciation: first ape, then man, then gods. So there are two possible concepts: God..., and gods.
Assuming the correctness of Sitchin's hypotheses, a whole new light now shines on existentialism. If God really means gods, then man has, over time, distorted the meaning of the original word, and Sartre can rest securely on his laurels and in his beliefs. Sartre would say that there is now proof that there is no wondrous, etherial, supernatural God to give man essence prior to his existence and that such proof supports the implication that a man first exists and then creates his own essence, because the concept of God which has existed for so long was born and developed in mankind's own distorted imagination over the millennia.
Carnap, were he still alive, would now have empirical data with which to deal with propositions relating to the concept of God (or, more aptly, gods), and he would take those propositions out of the realm of metaphysics and place them into the realm of empirical science. Indeed, he could no longer dispute Sartre's ideas about existentialism because questions relating to a metaphysical God would no longer exist (there never was a God; there was only a species a step above homo sapiens known as gods).
Assuming the validity of Sitchin's writings, could philosophy in general dismiss all questions relating to the concept of God? There is one ingredient in his writings that I have not yet addressed.
The leaders of the gods on Earth held various ceremonies to commemorate certain events such as the New Year. As part of these ceremonies, the gods prayed! To what or to whom did they pray? Sartre and Carnap would have much to say about that.
Personal Reflections (Post Essay)
In support of Carnap, I choose to think that all the events in history that can be attributed to "God" can be explained in terms of natural, empirically verifiable processes. For example, the "rain of fire" that Moses predicted is attributed in the scientific community to a volcanic eruption that destroyed the 60,000 square-mile island of Santorini in the Mediterranean Sea at about the same time. Other such phenomena, such as "the rivers that ran red with blood," have similar natural explanations.
As for Sartre's existentialism, advances in the field of genetics are compiling evidence that tends to support the proposition that man is ruled far more by his genes than he is by a free will, and so Sartre would have either to modify severely his views on existentialism or to abandon them entirely, God notwithstanding.
Has the Earth been visited in eons past? I like to think so. That Sitchin believes we are a cross between a lesser and a greater species could answer more than a few questions about man's past. For example, the missing link has never been found because it simply never existed. Sitchin believes that the Anunnaki built the first three pyramids in Egypt to serve as guideposts to a landing strip for their spacecraft. He believes also that they built Stonehenge. Far more remarkable, he believes that that they are currently doing something on Mars, that they built the so called "face on Mars" and several features that have been described as pyramids (again as landing beacons), and he believes that the Russian Phobos spacecraft that was sent to Mars to study the moon Phobos and the Martian landscape was knocked out of orbit by an Anunnaki spacecraft (the Russians have a photo that could be interpreted as support for this hypothesis). Sitchin believes that the Anunnaki hierarchy of rulership evolved into the Greek and Roman pantheon and ultimately into the biblical God, Yahweh (Yahweh is ENLIL, first born of ANU, older brother of EN.KI, heir apparent to the Anunnaki throne). "Thou shalt have no other Gods before me!" What other Gods?
Finally, the metaphysical concept of God: is there indeed a God? Perhaps, but it is not some omnipotent father figure as understood from reading the bible. There are energy forces in nature that man has yet to fathom. for example, electricity is now known to be the movement of electrons through a conductor, a phenomenon that can be measured, described and understood, but while scientists know that there is a force in nature called gravity, they have not yet been able to break it down into its constituent parts, measure it and explain it. Likewise, there are forces in nature that man is extremely far from grasping whose effect has been demonstrated but can neither be explained nor measured at this time. Such phenomena as telepathy, precognition, hands-on healing, the power of prayer (questions regarding their validity are not within the scope of this discussion) are some aspects of these forces. That Christ existed is a matter of record. The He performed what have been described as miracles is also a matter of record. His relationship to God remains a question for the philosophers until such time that empirical science has either explained or explained away those forces in nature which are now considered supernatural and mataphysical.