The general appeal to the testimony of the senses is followed by four special arguments. According to the first of these, it is plain that perceptions are produced in us by exterior causes affecting our senses, "because those that want the organs of any sense never can have the ideas belonging to that sense produced in their minds." This is supposed to prove that they come in by the organs of that sense, and in no other way. But here again one may ask, What is meant by the organs of any sense? If the "real" external organ be meant, one may object that its existence has not yet been proved. If the organ immediately known be meant, one has only called attention to the fact that certain ideas are a _sine qua non_ to the existence of certain other ideas. How this tends to prove the existence of something distinct from ideas is not apparent. Locke's impulse in this argument finds its source in our common experience that bodily organs immediately perceived are proved by observation to be prerequisites to the experiencing of ideas. We see a given object in a certain relation to a normal human body, and we infer an idea of the object connected with that body. We say the man has an idea of the object, and can only infer the object itself. We connect the idea with some particular part of his body, and regard this as the medium through which he gains the idea. All this is reasonable enough. It is well to remember, however, that in all this the "real" object is not observed to play any part. The object which I certainly see in relation to the body which I certainly see is what Locke would call an idea. The man's body is an idea. The idea which I assume the man to have is to me, if I remain within the sphere of the observable, an idea of the (idea) object I see. If I am to get any "real" object at all it is not by reference to observation or experience. If I am to get it by inference, some ground must be furnished for inference. Again Locke has confounded the observable with the "real." It is only on this ground that the appeal to the sense organ has any force.