We do not, therefore, divide man from other animals, but rather assert that many proofs and subtle analyses show the identity of their intelligence in its fundamental elements, while the difference is only the result of a reaction of the same intelligence on itself. Such a theory does not in any way interrupt the natural evolution and genesis of the animal kingdom, while the distinctive peculiarity of man is shown in an act which, as I believe, clearly explains the new faculty of reason acquired by him. I must admit that in speaking of the psychical faculty as a force which possesses laws peculiar to itself, it has appeared to a learned and competent judge that I have conceded a real existence to this faculty, independently of the physiological conditions through which it manifests itself, which might be called a mythical personality in the constitution of the world. If I had really made such an assertion, it would be an error which I am perhaps more ready than others to repudiate, as it will appear in the present work. I am far from blaming the courteous critics who allege such objections to my theory, and indeed I am honoured by their notice. I must blame myself for not having, in my desire to be brief, sufficiently defined my conception. I hold the psychical manifestation to be not only conditioned by the organism, to speak scientifically, and to be rendered physiologically possible by these conditions, but I consider it to be of the same nature as the other so-called forces of the universe; such, for example, as the manifestations of light, of electricity, of magnetism, and the like. When physicists speak of these forces--if the necessities of language and the brevity of the explanation constrain us to adopt the term forces, as though they were real substances--they certainly do not believe, nor wish others to believe, that they are really such. It is well known that such expressions are used to signify the appearance under certain circumstances of some special phenomena which group themselves by their mode and power of manifestation into one generic conception as a summary of the whole. They always take place, relatively to these circumstances, in the same mode and with the same power, so that they may at once be experimentally distinguished from others which have been grouped together in like manner.