"A man is the resultant and exponent of all the forces that have been brought to bear upon him, whether before his birth or afterwards. His action at any moment depends solely upon his constitution, and on the intensity and direction of the various agencies to which he is, and has been, subjected. Some of these will counteract each other; but as he is by nature, and as he has been acted on, and is now acted on from without, so will he do, as certainly and regularly as though he were a machine. We do not generally admit this, because we do not know the whole nature of any one, nor the whole of the forces that act upon him. We see but a part, and being thus unable to generalise human conduct, except very roughly, we deny that it is subject to any fixed laws at all, and ascribe much both of a man's character and actions to chance, or luck, or fortune; but these are only words whereby we escape the admission of our own ignorance; and a little reflection will teach us that the most daring flight of the imagination or the most subtle exercise of the reason is as much the thing that must arise, and the only thing that can by any possibility arise, at the moment of its arising, as the falling of a dead leaf when the wind shakes it from the tree."