supposed two persons, each of whom experiences a visual perception. One looks at one object, the other at another; but both are looking with the same organs of sense, that is, with their eyes. How is it possible to understand that these eyes can, in turn, according to the necessity of the moment, see the two faces, physical and mental, of the same object?
They are the two faces of an identical object, is the answer made to us, because the two visions, although applied to the same object, are essentially different. On the one hand is a sensation of displacement, of movement, of a dance executed by the molecules of some proteid substance; on the other hand is a flock of sheep passing over the plain at a distance of a hundred metres away.
It seems to me that here also the argument advanced is not sound. In the first place, it is essential to notice that not only are the two paths of cognition identical, but also that the perceptions are of the same nature. There is in this no opposition between the physical and the mental. What is compared are the two phenomena, which are both mixed and are physico-mental—physical, through the object to which they are applied, mental, through the act of cognition they imply. To perceive an object in the plain and to perceive a dynamic state of the brain are two operations which each imply an act of cognition;
