same, to certain brain centers), but as of something that is made up of content, which is evidently regarded as the intrinsic nature of certain "states of consciousness". Later on we shall see that this whole argument is really meaningless; but before we proceed to show this we will for some time remain on a level on which there seems to be some sense in phrases of this sort. This will involve the use of incorrect language on our part, but for the sake of clarity we shall not be afraid of it and shall add the necessary corrections in due time.
The above argument, or a similar one, occurs in many metaphysical discussions, and we shall have to explain later that it must be regarded as the typical argument in metaphysics. The metaphysicians who use it ascribe to it the character of an inference by analogy and are therefore willing to admit that the conclusion is not absolutely certain. They say that it is just "highly probable" that the visual perceptions of two individuals have practically the same content when they look at the same object and are both in possession of sound eyes and optical nerves and brain centres. We declare ourselves satisfied with this admission and call our philosopher's attention to the fact that, according to him, there is a possibility, however faint, that the content of one person's visual perception may be altogether different from that of another person's. He would have to admit that possibly the content which arises in the first man's mind when he is looking at something might be similar to, or even the same as, the content of the perceptions which arise in the second man's mind when he is listening to something.
In other words: what the first person calls "colour" would be called "sound" by the second person, if he could experience the content of the first one. If the second man could suddenly enter into the first one's mind he might exclaim: "Oh, now I am hearing with my eyes and seeing with my ears!" (The reader will bear in mind that I am speaking as if there were real meaning in the metaphysicians' first argument.)
Now, since such an exchange of personalities cannot possibly take place (and this impossibility is not just an empirical or a practical one, but, as we shall understand later, a logical impossibility, i.e. there is no sense in the assumption) the supposed difference of content could never be discovered as long as we assume the order and structure of all the perceptions to remain the same. For this assumption means that all reactions by which
