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 the physical to the mental. What characterises materialist philosophy is its belief in the possibility of such a passage, and its considering it as the genesis of thought. “One calls materialist,” says Renouvier, with great exactness, “every philosophy which defines thought as the product of a compound whose elements do not imply thought.” A sweeping formula which allows us to foresee all the future avatars of the materialist doctrine, and to class them beforehand in the same category.

The criticisms which have been directed against materialism are all, or nearly all, variations of the principle of heterogeneity. We will not dwell long on this, but simply recollect that, according to this principle, it is impossible to attribute to the brain the capacity of generating consciousness. Physical force can indeed generate physical force under the same or a different form, and it thus produces all the effects which are determined by the laws of nature. But it is impossible to comprehend how physical force can enrich itself at a given moment by a conscious force. Physical force is reduced to movements of bodies and to displacements of atoms; how could a change of position in any inert objects give rise to a judgment, a reasoning, or any phenomenon of the consciousness? It is further said: this idea of function, which materialists