In order to show this, it is necessary that the idea of evolution should be used fearlessly, and applied to all facts that can in any way come under it.  It must, in other words, be used as a category of thought, whose application is universal; so that, if it is valid at all as a theory, it is valid of all finite things.  For the question we are dealing with is not the truth of the hypothesis of a particular science, but the truth of a hypothesis as to the relation of all objects in the world, including man himself.  We must not be deterred from this universal application by the fact that we cannot, as yet, prove its truth in every detail.  No scientific hypothesis ever has exhausted its details.  I consider, therefore, that Mr. Tyndall had a complete right to “cross the boundary of the experimental evidence by an intellectual necessity”; for the necessity comes from the assumption of a possible explanation by the aid of the hypothesis.  It is no argument against such a procedure to insist that, as yet, there is no proof of the absolute continuity of matter and physical life, or that the dead begets the living.  The hypothesis is not disproved by the absence of evidence; it is only not proved.  The connection may be there, although we have not, as yet, been able to find it.  In the face of such difficulties as these, the scientific investigator has always a right to claim more time; and his attitude is impregnable as long as he remembers, as Mr. Tyndall did on the whole, that his hypothesis is a hypothesis.

But Mr. Tyndall has himself given up this right.  He, like Mr. Huxley, has placed the phenomena of self-consciousness outside of the developing process, and confined the sphere in which evolution is applicable, to natural objects.  Between objects and the subject, even when both subject and object are man himself, there lies “an impassable gulf.”

Even to try “to comprehend the connection between thought and thing is absurd, like the effort of a man trying to lift himself by his own waist-band.”  Our states of self-consciousness are symbols only—­symbols of an outside entity, whose real nature we can never know.  We know only these states; we only infer “that anything answering to our impressions exists outside of ourselves.”  And it is impossible to justify even that inference; for, if we can only know states of consciousness, we cannot say that they are symbols of anything, or that there is anything to be symbolized.  The external world, on this theory, ceases to exist even as an unknown entity.  In triumphantly pointing out that, in virtue of this psychological view, “There is, you will observe, no very rank materialism here,” Mr. Tyndall forgets that he has destroyed the basis of all natural science, and reduced evolution into a law of “an outside entity,” of which we can never know anything, and any inference regarding which violates every law of thought.