When we come to the brutes, the case is distinctly worse.  We think that we can attain to some notion of the minds to be attributed to such animals as the ape, the dog, the cat, the horse, and it is not nonsense to speak of an animal psychology.  But who will undertake to tell us anything definite of the mind of a fly, a grasshopper, a snail, or a cuttlefish?  That they have minds, or something like minds, we must believe; what their minds are like, a prudent man scarcely even attempts to say.  In our distribution of minds may we stop short of even the very lowest animal organisms?  It seems arbitrary to do so.

More than that; some thoughtful men have been led by the analogy between plant life and animal life to believe that something more or less remotely like the consciousness which we attribute to animals must be attributed also to plants.  Upon this belief I shall not dwell, for here we are evidently at the limit of our knowledge, and are making the vaguest of guesses.  No one pretends that we have even the beginnings of a plant psychology.  At the same time, we must admit that organisms of all sorts do bear some analogy to each other, even if it be a remote one; and we must admit also that we cannot prove plants to be wholly devoid of a rudimentary consciousness of some sort.

As we begin with man and descend the scale of beings, we seem, in the upper part of the series, to be in no doubt that minds exist.  Our only question is as to the precise contents of those minds.  Further down we begin to ask ourselves whether anything like mind is revealed at all.  That this should be so is to be expected.  Our argument for other minds is the argument from analogy, and as we move down the scale our analogy grows more and more remote until it seems to fade out altogether.  He who harbors doubts as to whether the plants enjoy some sort of psychic life, may well find those doubts intensified when he turns to study the crystal; and when he contemplates inorganic matter he should admit that the thread of his argument has become so attenuated that he cannot find it at all.

43.  THE DOCTRINE OF MIND-STUFF.—­Nevertheless, there have been those who have attributed something like consciousness even to inorganic matter.  If the doctrine of evolution be true, argues Professor Clifford,[4] “we shall have along the line of the human pedigree a series of imperceptible steps connecting inorganic matter with ourselves.  To the later members of that series we must undoubtedly ascribe consciousness, although it must, of course, have been simpler than our own.  But where are we to stop?  In the case of organisms of a certain complexity, consciousness is inferred.  As we go back along the line, the complexity of the organism and of its nerve-action insensibly diminishes; and for the first part of our course we see reason to think that the complexity of consciousness insensibly diminishes also.  But if we make a jump, say to the tunicate mollusks, we see no reason there to infer the existence of consciousness at all.  Yet not only is it impossible to point out a place where any sudden break takes place, but it is contrary to all the natural training of our minds to suppose a breach of continuity so great.”