"Hear my relation, then. When I was a young man, Cebes, I was wonderfully desirous of that wisdom which they call a history of nature; for it appeared to me to be a very sublime thing to know the causes of every thing--why each thing is generated, why it perishes, and why it exists. And I often tossed myself upward and downward, considering first such things as these, whether when heat and cold have undergone a certain corruption, as some say, then animals are formed; and whether the blood is that by means of which we think, or air, or fire, or none of these, but that it is the brain that produces the perceptions of hearing, seeing, and smelling; and that from these come memory and opinion; and from memory and opinion, when in a state of rest, in the same way knowledge is produced. 103. And, again, considering the corruptions of these, and the affections incidental to the heavens and the earth, I at length appeared to myself so unskillful in these speculations that nothing could be more so. But I will give you a sufficient proof of this; for I then became, by these very speculations, so very blind with respect to things which I knew clearly before, as it appeared to myself and others, that I unlearned even the things which I thought I knew before, both on many other subjects and also this, why a man grows. For, before, I thought this was evident to every one--that it proceeds from eating and drinking; for that, when, from the food, flesh is added to flesh, bone to bone, and so on in the same proportion, what is proper to them is added to the several other parts, then the bulk which was small becomes afterward large, and thus that a little man becomes a big one. Such was my opinion at that time. Does it appear to you correct?" "To me it does," said Cebes. 104. "Consider this further. I thought that I had formed a right opinion, when, on seeing a tall man standing by a short one, I judged that he was taller by the head, and in like manner, one horse than another; and, still more clearly than this, ten appeared to me to be more than eight by two being added to them, and that two cubits are greater than one cubit by exceeding it a half." "But now," said Cebes, "what think you of these matters?"