Indeed this demonstration has shown that the successive advance through the three stages, in invariable order, was the necessary form of progress of the human mind in the knowledge of phenomena. It is founded upon the nature of the mind. In Comte’s thought, the law of the three states could therefore have been equally called psychological or historical. But we are not here concerned with introspective Psychology, which uses self-consciousness as a means of investigation. Comte does not recognize any scientific value in this method.[22] He even denies its possibility. Moreover the observation of a subject by himself, were it possible, would be of no help in the present case. For it would only reveal to him the present state of his individual intellect, and not the law of the evolution of the human mind. For this law to become manifest, we must consider not the individual, but the species. Giving up a fruitless effort at self-contemplation in its activity, the intellect must grasp the law of its successive phases in the progress of what it has produced. The philosophical history of our beliefs, of our conceptions, and of our systems: such is the consciousness which the human intellect can have of itself. There only, the philosopher sees the faculties of which this intellect contained the germ coming into play by turns, to reach a “durable harmony.” Then, once discovered, the law of the three States helps us to understand the intellectual evolution of each individual, and the study of the individual then furnishes us with a supplementary verification of the law. But, by itself, this study of the individual could not have established it. Whatever utility I may have often derived from the consideration of the individual, says Comte, it is evidently to the direct study of the species that I owed, not only the fundamental thought in my theory, but afterwards its specific development. The law of the three States is then the general formula of the progress of the human intellect, considered not in an individual subject, but in the _universal subject_, which is humanity.