Before Hume, many philosophers made exceptions for metaphysics or held it to different standards than other areas of inquiry. Hume insisted that metaphysical issues, such as the existence of God, the possibility of miracles, and immortality of the soul, be held up to the same process of inquiry as investigations in the realm of ethics or physical science. For example, we can logically say that we can’t conceive of what life might be like on a planet with no oxygen because our experience involves only forms of life that utilize oxygen. Why, then, should we allow for the existence of a being such as God, which is supposed to be the only example of his kind? We have no experience of anything even remotely like what we suppose God to be. We cannot assume that the existence of the universe automatically proves the existence of a creator because we have no experience that tells us that this has been proven. By this reasoning, the concept of God has no real meaning, and we cannot rationally accept it as certain.