[167] for the great darkness which is spread over all existing bodies and things does not permit one to see the real nature of each thing, but even if any one, under the influence of immoderate curiosity or of a real love of learning, wishes to emerge from ignorance and to obtain a closer view, he, like people wholly deprived of sight, stumbling over what is before his feet, will fall, and so get behind hand before he can lay hold of anything; or else, snatching at something with his hands, [76] he will make uncertain guesses, having only conjecture in the place of truth.