"I believe that the first step in the setting of a "real external world" is the formation of the concept of bodily objects... Out of the multitude of our sense experiences we take, mentally and arbitrarily, certain repeatedly occurring complexes of sense impressions... and we correlate to them a concept—the concept of a bodily object. Considered logically, this concept is not identical with the totality of sense impressions referred to; but it is a free creation of the human (or animal) mind. ...by means of such concepts and mental relations between them, we are able to orient ourselves in the labyrinth of sense impressions. These notions and relations, although free mental creations, appear to us stronger and more unalterable than the individual sense experience itself, the character of which... is never completely guaranteed."