It is true that water will flow indifferently to east and west, but will it flow equally well up and down? Human nature is disposed toward goodness, just as water tends to flow downwards. There is no water but flows downwards, and no man but shows his tendency to be good. Now, by striking water hard, you may splash it higher than your forehead, and by damming it, you may make it go uphill. But, is that the nature of water? It is external force that causes it to do so. Likewise, if a man is made to do what is not good, his nature is being similarly forced.
