The second difficulty spoken of consists in the fact that, accepting the view which regards the brain as the mind’s tool, we cannot well avoid regarding the mind as a kind of ghost or demon, similar to the demons with which the imagination of primitive peoples populates the universe--gaseous and usually invisible men, women, giants, or dwarfs. Mankind has always felt strongly inclined to believe in the existence of such demons, and is still fond of making them the subjects of fairy tales and similar stories. But the more mature experience of the last centuries of human history has eliminated them from our theories of the actual world and assigned them their proper places in tales and mythology. Winter and summer, rain and sunshine, even the organic processes in the heart or the spinal cord are understood only by excluding from the explanation the assumption of such demons. The same is by analogy true for the processes in the brain, for the brain is not likely to be an exception to the rule. It is more difficult, of course, to determine directly whether such a demon exerts his influence in the inaccessible cavity of the skull than it is on the street or even in a haunted house. But no assertion is entitled to be regarded as true merely because we cannot go to the place in question and observe that it is false. Why not assert that heaven is located on the back side of the moon and hell in the center of the sun, merely because no one can see with his own eyes that they are not there? We must make only those assumptions which, considered from all points of view, have a high degree of probability, not those which flatter our vanity or appeal to us as the fashionable belief of the time. Now, it does not seem probable that our brain is the residence of a separable demon, no matter whether we attribute to him the power of changing at will the total amount of energy contained in our body, or conceive his activity, as some psychologists do, as a new form of energy added to the mechanical, thermal, electric, chemical, and so on,--requiring only an additional transformation of energy and not breaking down the principle of its conservation. 2. _The Brain an Objectified Conception of the Mind_