Therefore, Kant proposes a new basis for a science of metaphysics, posing the question: how is a science of metaphysics possible, if at all? According to Kant, only practical reason, the faculty of moral consciousness, the moral law of which everyone is immediately aware, makes it possible to know things as they are. This led to his most influential contribution to metaphysics: the abandonment of the quest to try to know the world as it is "in itself" independent of sense experience. He demonstrated this with a thought experiment, showing that it is not possible to meaningfully conceive of an object that exists outside of time and has no spatial components and is not structured in accordance with the categories of the understanding ("Verstand"), such as substance and causality. Although such an object cannot be conceived, Kant argues, there is no way of showing that such an object does not exist. Therefore, Kant says, the science of metaphysics must not attempt to reach beyond the limits of possible experience but must discuss only those limits, thus furthering the understanding of ourselves as thinking beings. The human mind is incapable of going beyond experience so as to obtain a knowledge of ultimate reality, because no direct advance can be made from pure ideas to objective existence.