The whole matter will be more fully discussed in Chapter XI.  This chapter I shall close with a brief summary of the points which the reader will do well to bear in mind when he occupies himself with parallelism.

(1) Parallelism is a protest against the interactionist’s tendency to materialize the mind.

(2) The name is a figurative expression, and must not be taken literally.  The true relation between mental phenomena and physical is given in certain common experiences that have been indicated, and it is a unique relation.

(3) It is a fixed and absolutely dependable relation.  It is impossible that there should be a particular mental fact without its corresponding physical fact; and it is impossible that this physical fact should occur without its corresponding mental fact.

(4) The parallelist objects to calling this relation causal, because this obscures the distinction between it and the relation between facts both of which are physical.  He prefers the word “concomitance.”

(5) Such objections to parallelism as that cited above assume that the concomitance of which the parallelist speaks is analogous to physical concomitance.  The chemist puts together a volume of hydrogen gas and a volume of chlorine gas, and the result is two volumes of hydrochloric acid gas.  We regard it as essential to the result that there should be the two gases and that they should be brought together.  But the fact that the chemist has red hair we rightly look upon as a concomitant phenomenon of no importance.  The result would be the same if he had black hair or were bald.  But this is not the concomitance that interests the parallelist.  The two sorts of concomitance are alike only in the one point.  Some phenomenon is regarded as excluded from the series of causes and effects under discussion.  On the other hand, the difference between the two is all-important; in the one case, the concomitant phenomenon is an accidental circumstance that might just as well be absent; in the other, it is nothing of the sort; it cannot be absent—­the mental fact must exist if the brain-change in question exists.

It is quite possible that, on reading this list of points, one may be inclined to make two protests.

First:  Is a parallelism so carefully guarded as this properly called parallelism at all?  To this I answer:  The name matters little.  I have used it because I have no better term.  Certainly, it is not the parallelism which is sometimes brought forward, and which peeps out from the citation from Clifford.  It is nothing more than an insistence upon the truth that we should not treat the mind as though it were a material thing.  If any one wishes to take the doctrine and discard the name, I have no objection.  As so guarded, the doctrine is, I think, true.