and because, secondly, they exhibit the acts, and other outward signs, which in my own case I know by experience to be caused by feelings.  I am conscious in myself of a series of facts connected by a uniform sequence, of which the beginning is modifications of my body, the middle is feelings, the end is outward demeanor.  In the case of other human beings I have the evidence of my senses for the first and last links of the series, but not for the intermediate link.  I find, however, that the sequence between the first and last is as regular and constant in those other cases as it is in mine.  In my own case I know that the first link produces the last through the intermediate link, and could not produce it without.  Experience, therefore, obliges me to conclude that there must be an intermediate link; which must either be the same in others as in myself, or a different one.  I must either believe them to be alive, or to be automatons; and by believing them to be alive, that is, by supposing the link to be of the same nature as in the case of which I have experience, and which is in all respects similar, I bring other human beings, as phenomena, under the same generalizations which I know by experience to be the true theory of my own existence.  And in doing so I conform to the legitimate rules of experimental inquiry.  The process is exactly parallel to that by which Newton proved that the force which keeps the planets in their orbits is identical with that by which an apple falls to the ground.  It was not incumbent on Newton to prove the impossibility of its being any other force; he was thought to have made out his point when he had simply shown that no other force need be supposed.  We know the existence of other beings by generalization from the knowledge of our own; the generalization merely postulates that what experience shows to be a mark of the existence of something within the sphere of our consciousness, may be concluded to be a mark of the same thing beyond that sphere.”

Now, the plain man accepts the argument from analogy, here insisted upon, every day of his life.  He is continually forming an opinion as to the contents of other minds on a basis of the bodily manifestations presented to his view.  The process of inference is so natural and instinctive that we are tempted to say that it hardly deserves to be called an inference.  Certainly the man is not conscious of distinct steps in the process; he perceives certain phenomena, and they are at once illuminated by their interpretation.  He reads other men as we read a book—­the signs on the paper are scarcely attended to, our whole thought is absorbed in that for which they stand.  As I have said above, the psychologist accepts the argument, and founds his conclusions upon it.

Upon what ground can one urge that this inference to other minds is a doubtful one?  It is made universally.  We have seen that even those who have theoretic objections against it, do not hesitate to draw it, as a matter of fact.  It appears unnatural in the extreme to reject it.  What can induce men to regard it with suspicion?