the consciousness of an extension out of thyself, proceeds from the consciousness of thine own extension as a material body, and is conditioned by it. But then thou must, in the first place, explain this extension of thy material body.
I. It is enough. I now perceive clearly that I neither see nor feel the superficial extension of the properties of bodies, nor apprehend it by any other sense. I see that it is my constant practice to extend over a surface, what nevertheless in sensation is but one point; to represent as adjacent and simultaneous, what I ought to represent only as successive, since in mere sensation there is nothing simultaneous, but all is successive. I discover that I proceed in fact exactly as the geometer does in the construction of his figures, extending points to lines, and lines to surfaces. I am astonished how I should have done this.
Spirit. Thou dost more than this, and what is yet more strange. This surface which thou attributest to bodies, thou canst indeed neither see nor feel, nor perceive by any organ; but it may be said, in a certain sense, that thou canst see the red colour upon it, or feel the smoothness. But thou addest something more even to this surface: thou extendest it to a solid mathematical figure; as by thy previous admission thou hast extended the line to a surface. Thou assumest a substantial interior existence of the body behind its surface. Tell me, canst thou then see, feel, or recognise by any sense, the actual presence of anything behind this surface?
I. By no means:—the space behind the surface is impenetrable to my sight, touch, or any of my senses.
Spirit. And yet thou dost assume the existence of
