Democritus, however, neglecting the final cause, reduces to necessity all the operations of Nature.Now they are necessary, it is true, but yet they are for a final cause and for the sake of what is best in each case.Thus nothing prevents the teeth from being formed and being shed in this way; but it is not on account of these causes but on account of the end (or final cause); these are causes only in the sense of being the moving and efficient instruments and the material.So it is reasonable that Nature should perform most of her operations using breath as an instrument, for as some instruments serve many uses in the arts, e.g.the hammer and anvil in the smith's art, so does breath in the living things formed by Nature.But to say that necessity is the only cause is much as if we should think that the water has been drawn off from a dropsical patient on account of the lancet, not on account of health, for the sake of which the lancet made the incision.
We have thus spoken of the teeth, saying why some are shed and grow again, and others not, and generally for what cause they are formed.And we have spoken of the other affections of the parts which are found to occur not for any final end but of necessity and on account of the motive or efficient cause.
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