Moreover, there is a break in the whole argument. I can follow the processes in my organism up to those in my brain, even though my assumptions become more and more hypothetical as I approach the central processes of the brain. The method of external observation ceases with the process in my brain, more particularly with the process which I should observe, if I could treat the brain with the instruments and methods of Physics and Chemistry. The method of internal observation, or introspection, begins with the sensations, and includes the construction of things out of the material of sense-data. At the point of transition from brain process to sensation, there is a break in the sequence of observation. The theory which I have here described, and which calls itself Critical Idealism, in contrast to the standpoint of naïve common sense which it calls Naïve Realism, makes the mistake of characterising one group of percepts as ideas, whilst taking another group in the very same sense as the Naïve Realism which it apparently refutes. It establishes the ideal character of percepts by accepting naïvely, as objectively valid facts, the percepts connected with one's own body; and, in addition, it fails to see that it confuses two spheres of observation, between which it can find no connecting link. Critical Idealism can refute Naïve Realism only by itself assuming, in naïve-realistic fashion, that one's own organism has objective existence. As soon as the Idealist realises that the percepts connected with his own organism stand on exactly the same footing as those which Naïve Realism assumes to have objective existence, he can no longer use the former as a safe foundation for his theory. He would, to be consistent, have to regard his own organism also as a mere complex of ideas. But this removes the possibility of regarding the content of the perceptual world as a product of the mind's organisation. One would have to assume that the idea "colour" was only a modification of the idea "eye." So-called Critical Idealism can be established only by borrowing the assumptions of Naïve Realism. The apparent refutation of the latter is achieved only by uncritically accepting its own assumptions as valid in another sphere. This much, then, is certain: Analysis within the world of percepts cannot establish Critical Idealism, and, consequently, cannot strip percepts of their objective character.