It seems to me quite plain that either this psychological theory, which Mr. Tyndall has mistaken for a philosophy, is invalid; or else it is useless to endeavour to propound any view regarding a “nature which is the phantom of the individual’s mind.”  I prefer the science of Mr. Tyndall (and of Mr. Huxley, too) to his philosophy; and he would have escaped materialism more effectively, if he had remained faithful to his theory of evolution.  It is a disloyalty, not only to science, but to thought, to cast away our categories when they seem to imply inconvenient consequences.  They must be valid universally, if they are valid at all.

Mr. Tyndall contends that nature makes man, and he finds evidence in the fact that we eat and drink, “of the control of mind by matter.”  Now, it seems to me, that if nature makes man, then nature makes man’s thoughts also.  His sensations, feelings, ideas, notions, being those of a naturally-evolved agent, are revelations of the potency of the primal matter, just as truly as are the buds, flowers, and fruits of a tree.  No doubt, we cannot as yet “comprehend the connection” between nervous action and sensation, any more than we can comprehend the connection between inorganic and organic existence.  But, if the absence of “experimental evidence” does not disprove the hypothesis in the one case, it can not disprove it in the other.  There are two crucial points in which the theory has not been established.

But, in both cases alike, there is the same kind of evidence that the connection exists; although in neither case can we, as yet, discover what it is.  Plants live by changing inorganic elements into organic structure; and man is intelligent only in so far as he crosses over the boundary between subject and object, and knows the world without him.  There is no “impassable gulf separating the subject and object”; if there were we could not know anything of either.  There are not two worlds—­the one of thoughts, the other of things—­which are absolutely exclusive of each other, but one universe in which thought and reality meet.  Mr. Tyndall thinks that it is an inference (and an inference over an impassable gulf!) that anything answering to our impressions exists outside ourselves.  “The question of the external world is the great battleground of metaphysics,” he quotes approvingly from Mr. J.S.  Mill.  But the question of the external world is not whether that world exists; it is, how are we to account for our knowledge that it does exist.  The inference is not from thoughts to things, nor from things to thoughts, but from a partially known world to a systematic theory of that world.  Philosophy is not engaged on the foolish enterprise of trying to discover whether the world exists, or whether we know that it exists; its problem is how to account for our knowledge.  It asks what must the nature of things be, seeing that they are known; and what is the nature of thought, seeing that it knows facts?