between the ideas of sight and touch, between the visible and tangible eye; for certainly on the tangible eye nothing either is or seems to be painted. Again, the visible eye, as well as all other visible objects, hath been shown to exist only in the mind; which, perceiving its own ideas, and comparing them together, does call some pictures in respect to others. What hath been said, being rightly comprehended and laid together, does, I think, afford a full and genuine explanation of the erect appearance of objects—which phenomenon, I must confess, I do not see how it can be explained by any theories of vision hitherto made public. In treating of these things, the use of language is apt to occasion some obscurity and confusion, and create in us wrong ideas. For, language, being accommodated to the common notions and prejudices of men, it is scarce possible to deliver the naked and precise truth, without great circumlocution, impropriety, and (to an unwary reader) seeming contradictions.[1]
That is to say, Berkeley insists upon the necessity for another and more concrete analysis than that afforded by the resources of descriptive language.
Later, in "The Principles of Human Knowledge," Part I., he seems to indicate that this profounder analysis must take a physiological direction:
The philosophic consideration of motion doth not imply the being of an absolute Space, distinct from that which is perceived by sense, and related to bodies.... When I excite a motion in some part of my body, if it be free or without resistance, I say there is Space. But if I find a resistance, then I say there is Body: and in proportion as the resistance to motion is lesser or greater, I say the space is more or less pure.... When, therefore, supposing all the world to be annihilated besides my own body, I say there still remains pure Space; thereby nothing else is meant but only that I conceive it possible for the limbs of my body to be moved on all sides without the least resistance: but if that too were annihilated then there could be no motion, and consequently no Space.[2]
Knowing little of physiology, Berkeley leaves the problem, stated so far, indeed, but only stated. It is this: How can we derive space, a general condition of external objects, from states of the body which, in their very nature, differ utterly from this, their product? Twenty-two years later, he returns to the question, and appears to raise it in fresh form. In the Fourth Dialogue of "Alciphron, the Minute Philosopher," he says:
(Euphranor speaks:) "We perceive distance, not immediately, but by mediation of a sign, which hath no likeness to it, or necessary connection with it, but only suggests it from repeated experience, as words do things." (Alciphron replies:) "Hold, Euphranor: now I think of it, the writers in optics tell us of an angle made by the two optic axes, where they meet in the visible point or object; which angle, the obtuser it is the nearer it shows the object to be, and by how much the acuter, by so much the farther off; and this from a necessary demonstrable connection."[3]
It is needless to add that Berkeley, although he makes physiological reference and research inevitable, lived long before such a study of "local signs" as that undertaken by Lotze was practicable.
