=Sensation Implies Externality.=--When, however, a sensory image, such as smooth, yellow, cold, etc., arises in consciousness as a result of the mind reacting when an external stimulus is applied to some sense organ, it is evident that, at least after very early infancy, one never has the image without at once referring it to some external cause. If, for instance, a person is but half awake and receives a sound sensation, he does not ask himself, "What mental state is _this_?" but rather, "What is _that_?" This shows an evident tendency to refer our sensations at once to an external cause, or indicates that our sensations always carry with them an implicit reference to an external object. Leaving, therefore, to the scientific psychologist to consider whether it is possible to have a pure sensation, we shall treat sensation as the recognition of a quality which is at least vaguely referred to an external object. In other words, sensation is a medium by which we are brought into relation with real things existing independently of our sensations. =Perception Involves Sensation Element.=--Moreover, an object is perceived as present here and now only because it is revealed to us through one or more of the senses. When, for instance, I reach out my hand in the dark room and receive a sensation of touch, I perceive the table as present before me. When I receive a sensation of sound as I pass by the church, I perceive that the organ is being played. When I receive a colour sensation from the store window, I say that I perceive oranges. Perception, therefore, involves the referring of the sensuous state, or image, to an external thing, while in adult life sensation is never accepted by our attention as satisfactory unless it is referred to something we regard as immediately presenting itself to us by means of the sensation. It is on account of this evident interrelation of the two that we speak of a process of sense perception.