It has also been said: it is by no means certain that any nervous mechanism can be invented which imitates and, if need were, could replace an intellectual act. For instance, what association of nerve cells, what molecular action, can imitate an act of comparison which enables us to see a resemblance between two objects? Let it be supposed, for example, that the resemblance of two impressions come from a partial identity, and that the latter has for material support an identity in the seat or the form of the corresponding nervous influx. But what is identity? How can it be conceived without supposing resemblance, of which it is but a form? How, then, can the one be explained by the other? Thus, for instance, at the bottom of all our intellectual acts, there is a certain degree of belief. Can any material combination be found which corresponds thereto? There is one last objection, the most serious of all. Parallelism, by establishing a fixed and invariable relation between the physical and the moral, ends by denying the role of this last, since the physical mechanism is sufficient to draw to itself all the effects which general belief attributes to the moral. The parallelists on this point go very much further than the materialists; the latter at least concede that the consciousness is of some use, since they compared it to a function or a secretion, and, after all, a secretion is a useful liquid. The parallelists are so strongly convinced that mechanism is alone efficacious that they come to deny any role to thought. The consciousness for them has no purpose: yet it keeps company with its object. The metaphors which serve to define it, part of which have been imagined by Huxley, are all of a passive nature. Such is the light, or the whistling noise which accompanies the working of an engine, but does not act on its machinery. Or, the shadow which dogs the steps of the traveller. Or a phosphorescence lighting up the traces of the movements of the brain. It has also been said that the consciousness is a useless luxury. Some have even gone further, and the fine and significant name of _epiphenomenon_, that has been given to thought, well translates that conception, according to which semi-realities may exist in nature. All these objections certainly carry great weight, but they are not capable of killing the doctrine--they only scotch it. I think there is a radical vice in parallelism, which till now has not been sufficiently indicated, and I ask what can really remain of the whole edifice when this vice has been once exposed? Parallelism implies a false idea, which we have already come across when discussing materialism. It is the idea that a phenomenon of consciousness constitutes one complete whole.