59.  I have just shown how the action of the will depends upon its causes; that there is nothing so appropriate to human nature as this dependence of our actions; and that otherwise one would slip into a preposterous and unendurable fatality, namely into the Fatum Mahometanum, which is the worst of all because it overthrows foresight and good counsel.  It is well to show, notwithstanding, how this dependence of voluntary actions does not fundamentally preclude the existence within us of a wonderful spontaneity, which in a certain sense makes the soul in its resolves independent of the physical influence of all other creatures.  This spontaneity, hitherto little recognized, which exalts our command over our actions to the highest pitch, is a consequence of the System of Pre-established Harmony, of which I must give some explanation here.  The Scholastic philosophers believed that there was a reciprocal physical influence between body and soul:  but since it has been recognized that thought and dimensional mass have no mutual connexion, and that they are creatures differing toto genere, many moderns have acknowledged that there is no physical communication between soul and body, despite the metaphysical communication always subsisting, which causes soul and body to compose one and the same suppositum, or what is called a person.  This physical communication, if there were such, would cause the soul to change the degree of speed and the directional line of some motions that are in the body, and vice versa the body to change the sequence of the thoughts that are in the soul.  But this effect cannot be inferred from any notion conceived in the body and in the soul; though nothing be better known to us than the soul, since it is inmost to us, that is to say inmost to itself.

[156] 60.  M. Descartes wished to compromise and to make a part of the body’s action dependent upon the soul.  He believed in the existence of a rule of Nature to the effect, according to him, that the same quantity of movement is conserved in bodies.  He deemed it not possible that the influence of the soul should violate this law of bodies, but he believed that the soul notwithstanding might have power to change the direction of the movements that are made in the body; much as a rider, though giving no force to the horse he mounts, nevertheless controls it by guiding that force in any direction he pleases.  But as that is done by means of the bridle, the bit, the spurs and other material aids, it is conceivable how that can be; there are, however, no instruments such as the soul may employ for this result, nothing indeed either in the soul or in the body, that is, either in thought or in the mass, which may serve to explain this change of the one by the other.  In a word, that the soul should change the quantity of force and that it should change the line of direction, both these things are equally inexplicable.