This principle bears the name of the _axiom of heterogeneity_, or the principle of _psycho-physical dualism_. No philosopher has more clearly formulated it, and more logically deduced its consequences, than Flournoy. This author has written a little pamphlet called _Metaphysique et Psychologie_, wherein he briefly sets forth all the known systems of metaphysics by reducing them to the so-called principle of heterogeneity; after this, the same principle enables him to "execute" them. He formulates it in the following terms: "body and mind, consciousness and the molecular cerebral movement of the brain, the psychical fact and the physical fact, although simultaneous, are heterogeneous, unconnected, irreducible, and obstinately two."[41] The same author adds: "this is evident of itself, and axiomatic. Every physical, chemical, or physiological event, in the last resort, simply consists, according to science, in a more or less rapid displacement of a certain number of material elements, in a change of their mutual distances or of their modes of grouping. Now, what can there be in common, I ask you, what analogy can you see, between this drawing together or moving apart of material masses in space, and the fact of having a feeling of joy, the recollection of an absent friend, the perception of a gas jet, a desire, or of an act of volition of any kind?" And further on: "All that we can say to connect two events so absolutely dissimilar is, that they take place _at the same time_.... This does not mean that we wish to reduce them to unity, or to join them together by the link of causality ... it is impossible to conceive any real connection, any internal relation between these two unconnected things." Let us not hesitate to denounce as false this proposition which is presented to us as an axiom. On looking closely into it, we shall perceive that the principle of heterogeneity does not contain the consequences it is sought to ascribe to it. It seems to me it should be split up into two propositions of very unequal value: 1, the mind and body are heterogeneous; 2, by virtue of this heterogeneity it is not possible to understand any direct relation between the two. Now, if the first proposition is absolutely correct, in the sense that consciousness and matter are heterogeneous, the second proposition seems to us directly contrary to the facts, which show us that the phenomena of consciousness are incomplete phenomena. The consciousness is not sufficient for itself; as we have said, it cannot exist by itself. This again, if you like, is an axiom, or rather it is a fact shown by observation and confirmed by reflection. Mind and matter brought down to the essential, to the consciousness and its object, form a natural whole, and the difficulty does not consist in uniting but in separating them. Consider the following fact: "I experience a sensation, and I have consciousness of it." This is the coupling of two things--a sensation and a cognition.