But the error is rather a common one; and see to what injustice it may lead one.  It is concluded that the conception of matter is an obscure one; that we do not know clearly what we mean when we speak of the mass of a body; that there are disputes as to proper significance to be given to the words cause and effect; that the laws of motion, as they are at present formulated, do not seem to account satisfactorily for the behavior of all material particles.  From this it is inferred that we must give up the attempt to explain mechanically the order of physical things.

Now, suppose that it were considered a dangerous and heterodox doctrine, that the changes in the system of things are due to the activities of minds.  Would not those who now love to point out the shortcomings of the science of mechanics discover a fine field for their destructive criticism?  Are there no disputes as to the ultimate nature of mind?  Are men agreed touching the relations of mind and matter?  What science even attempts to tell us how a mind, by an act of volition, sets material particles in motion or changes the direction of their motion?  How does one mind act upon another, and what does it mean for one mind to act upon another?

If the science of mechanics is not in all respects as complete a science as it is desirable that it should be, surely we must admit that when we turn to the field of mind we are not dealing with what is clear and free from difficulties.  Only a strong emotional bias can lead a man to dwell with emphasis upon the difficulties to be met with in the one field, and to pass lightly over those with which one meets in the other.

One may, however, refuse to admit that the order of nature is throughout mechanical, without taking any such unreasonable position as this.  One may hold that many of the changes in material things do not appear to be mechanical, and that it is too much of an assumption to maintain that they are such, even as an article of faith.  Thus, when we pass from the world of the inorganic to that of organic life, we seem to make an immense step.  No one has even begun to show us that the changes that take place in vegetable and animal organisms are all mechanical changes.  How can we dare to assume that they are?

With one who reasons thus we may certainly feel a sympathy.  The most ardent advocate of mechanism must admit that his doctrine is a working hypothesis, and not proved to be true.  Its acceptance would, however, be a genuine convenience from the point of view of science, for it does introduce, at least provisionally, a certain order into a vast number of facts, and gives a direction to investigation.  Perhaps the wisest thing to do is, not to combat the doctrine, but to accept it tentatively and to examine carefully what conclusions it may seem to carry with it—­how it may affect our outlook upon the world as a whole.