it cannot be determined a priori and asserted dogmatically.  Until such investigation has been carried out, it behoves us to be undogmatic and not to allege more than the facts absolutely warrant, that is to say, a relation of correspondence.  Parallelism is far too simple an explanation to be a true one.  Before the International Congress, Bergson launched another attack on parallelism which caused quite a little sensation among those present.  Says M. E. Chartier, in his report:  La lecture de ce memoire, lecture qui commandait l’attention a provoque chez presque tous les auditeurs un mouvement de surprise et d’inquietude. [Footnote:  The paper Le Paralogisme psycho-physiologique is given in Revue de metaphysique et de morale, Nov., 1904, pp. 895-908.  The Discussion in the Congress is given on pp. 1027-1037.  This was reissued under the title Le Cerveau et la Pensee:  une illusion philosophique in the collected volume of essays and lectures, published in 1919, L’Energie spirituelle, pp. 203-223 (Mind-Energy).] He there set out to show that Parallelism cannot be consistently stated from any point of view, for it rests on a fallacious argument—­on a fundamental contradiction.  To grasp Bergson’s points in this argument, the reading of this paper in the original, as a whole, is necessary.  It is difficult to condense it and keep its clearness of thought.  Briefly, it amounts to this, that the formulation of the doctrine of Parallelism rests on an ambiguity in the terms employed in its statement, that it contains a subtle dialectical artifice by which we pass surreptitiously from one system of notation to another ignoring the substitution:  logically, we ought to keep to one system of notation throughout.  The two systems are:  Idealism and Realism.  Bergson attempts to show that neither of these separately can admit Parallelism, and that Parallelism cannot be formulated except by a confusion of the two—­by a process of mental see-sawing as it were, which of course we are not entitled to perform, Idealism and Realism being two opposed and contradictory views of reality.  For the Idealist, things external to the mind are images, and of these the brain is one.  Yet the images are in the brain.  This amounts to saying that the whole is contained in the part.  We tend, however, to avoid this by passing to a pseudo-realistic position by saying that the brain is a thing and not an image.  This is passing over to the other system of notation.  For the Realist it is the essence of reality to suppose that there are things behind representations.  Some Realists maintain that the brain actually creates the representation, which is the doctrine of Epiphenomenalism:  while others hold the view of the Occasionalists, and others posit one reality underlying both.  All however agree in upholding Parallelism.  In the hands of the Realist, the theory is equivalent to asserting that a relation between two terms is equal to one of them.  This involves contradiction and Realism then crosses over to the other system of notation.  It cannot do without Idealism:  science itself oscillates from the one system to the other.  We cannot admit Parallelism as a dogma—­as a metaphysical truth—­however useful it may be as a working hypothesis.