To prepare the born-blind to answer philosophical interrogatories truly, and then to put these interrogatories rightly, would have been a feat, he declares, not unworthy of the united talents of Newton, Descartes, Locke, and Leibnitz.

Unless the patient were placed in such conditions as this, Diderot thinks there would be more profit in questioning a blind person of good sense, than in the answers of an uneducated person receiving sight for the first time under abnormal and bewildering circumstances.[63] In this he was undoubtedly right.

If the experiment could be prepared under the delicate conditions proper to make it demonstrative evidence, it would be final.

But the experiment had certainly not been so prepared in his time, and probably never will be.[64] Read in the light of the rich and elaborate speculative literature which England is producing in our own day, Diderot's once famous Letter on the Blind seems both crude and loose in its thinking.

Yet considering the state of philosophy in France at the time of its appearance, we are struck by the acuteness, the good sense, and the originality of many of its positions.