I. We distinguish sleep from waking, even abstracting the objectiveness of the sensations.
II. We distinguish two orders of phenomena of sensation;—the one internal, the other external, here also abstracting their objectiveness.
III. The senses give us certainty of the existence of bodies.
IV. Sensations have no type in the external object of what they represent, except extension and motion.
V. Touch is not the basis or touch-stone of certainty.
VI. All that we know by means of the senses may be reduced to this; that there are external beings, that is to say, beings placed outside of ourselves, which are extended, subject to necessary laws, and which produce in us the effects which we call sensations.
[CHAPTER XVI.]
POSSIBILITY OF OTHER SENSES.
91. Lamennais writes: "Who can say that a sixth sense would not disturb the harmony of the others by a contrary impression? On what foundation could he deny it? If we suppose other senses different from those which nature gave us, might not our sensations and our ideas be different? Perhaps a slight modification in our organs would be sufficient to ruin our whole science. Perhaps there are beings so organized that their sensations are wholly opposed to ours, and what is true for us is false for them, and reciprocally. For, if we examine the matter closely, what necessary connection is there between our sensations and the reality? And if there were such a connection, how could the senses make it known to us?"[38]