The ontological version of atheism makes a claim about existing reality, arguing that “GOD” does not exist, and is not part of reality. For atheists, reality consists of natural forces, atoms, molecules, plants, animals, and humans, without GOD, in the sense that is commonly attributed to this concept (i.e. supernatural, omnipotent and all-knowing, who created the world).
This argument of course immediately begs the question: How does one know GOD does not exist? After all, making such a decisive ontological claim requires absolute certainty of its truth. Where does this certainty come from? Our two main sources of knowledge about reality are empirical experience and logic.
Is it possible to conclude through one of them that there is no GOD? Empirical experience cannot lead to such a conclusion. How can one prove empirically that GOD does not exist? Is it possible to scan all of space and time, all of reality, and claim that we have not found GOD in any place? Of course not.