does the action of objects excite desire or aver|sion? How shall we obtain a clear conception of the operation of that principle to which the senses communicate their notices? The senses are only the middle term between the action of objects and animal action. This principle, however, has the power of determining all our motions; for it can modify and alter the ani|mal action, and even sometimes counteract it, notwithstanding the impression of objects.With regard to man, whose nature is so dif|ferent from that of other animals, this question is difficult to solve; because the soul participates all our movements; and it is not easy to distin|guish the effects of this spiritual substance from those produced solely by the material part of our frame. Of this we can form no judgment but by analogy, and by comparing our actions to the natural operations of the other animals. But, as this spiritual substance has been conferred on man alone, by which he is enabled to think and reflect, and, as the brutes are purely material, and neither think nor reflect, and yet act, and seem to be determined by motives, we cannot hesitate in pronouncing the principle of motion in them to be perfectly mechanical, and to de|pend absolutely on their organization.I apprehend, therefore, that, in the animal, the action of objects on the senses produces an|other on the brain, which I consider as a ge|neral internal sense, that receives all the impres|sions 0