15. It is easy to comprehend why certain philosophers have maintained that all our ideas come from the senses, if we understand them to mean that sensations awaken our internal activity, and, so to speak, supply the intellect with materials: but it is not so easy to see how it can be advanced as a certain, clear, and exceedingly simple truth that there is in our mind nothing but these materials, these sensations. We have only to fix our attention for a moment upon what passes within us to discover many phenomena distinct from sensation, and various faculties which have nothing to do with sensation. If Condillac had been satisfied with maintaining that these faculties needed sensation as a kind of excitement in order to be developed, he would have advanced nothing contrary to sound philosophy: but for him to pretend that all that is excited and all that is developed is only the principle which excites, and to insist that this is confirmed by actual observation, is openly to contradict observation itself, and to render it absolutely impossible for him to make the least progress in the explanation of intellectual activity, unless he abandons the supposition upon which his whole system is founded. Nevertheless, the author of the _Treatise on Sensations_ seems to be perfectly satisfied with his system: the actual impression is the sensation; the recollection of the sensation is the intellectual idea. If this is not sound, it is at least deceptive: with the appearance of nice observation he stops at the surface of things, and does not fatigue the pupil. Every thing comes from sensation; but this is because Condillac makes his statue talk as he pleases, without paying the least attention to his hypothesis of sensation alone. 16. This system, by reason of its philosophical meagerness, is fatal to all moral ideas. What becomes of morality if there are no ideas, except sensations? What becomes of duty if every thing is reduced to sensible necessity, to pleasure or pain? And what becomes of God, and of all man's relations to God? CHAPTER III. DIFFERENCE BETWEEN GEOMETRICAL IDEAS AND THE SENSIBLE REPRESENTATIONS WHICH ACCOMPANY THEM. 17. Sensible representations always accompany our intellectual ideas. This is why in reflecting upon the latter we are apt to confound them with the former. We say, in reflecting upon them, not in making use of them. We none of us, have any trouble in making use of ideas according to circumstances; the error lies in the reflex, not in the direct act. It will be well to bear this last observation in mind.