Page:The System of Nature.djvu/149

 ideas, which give birth to this disposition are called motives, because they are the springs or movements which determine it to act, that is to say, which give play to the organs of the body. Thus, voluntary actions are the motion of the body, determined by the modification of the brain. Fruit hanging on a tree, through the agency of the visual organs, modifies the brain in such a manner as to dispose the arm to stretch itself forth to cull it; again, it modifies it in another manner, by which it excites the hand to carry it to the mouth.

All the modifications which the interior organ or the brain receives, all the sensations, all the perceptions, all the ideas that are generated by the objects which give impulse to the senses, or which it renews within itself by its own peculiar faculties, are either favourable or prejudicial to man's mode of existence, whether that be transitory or habitual: they dispose the interior organ to action, which it exercises by reason of its own peculiar energy: this action is not, however, the same in all the individuals of the human species, depending much on their respective temperaments. From hence the PASSIONS have their birth: these are more or less violent; they are, however, nothing more than the motion of the will, determined by the objects which give it activity; consequently composed of the analogy or of the discordance which is found between these objects, man's peculiar mode of existence, and the force of his temperament. From this it results, that the passions are modes of existence or modifications of the brain; which either attract or repel those objects by which man is surrounded; that consequently they are submitted