If one were to think of escaping from the toils of these investigations by saying that experience constantly offers examples of a regularity of appearances that give sufficient occasion for abstracting the concept of cause from them, and thereby at the same time thought to confirm the objective validity of such a concept, then one has not noticed that the concept of cause cannot arise in this way at all, but must either be grounded in the understanding completely a priori or else be entirely surrendered as a mere fantasy of the brain.