The historical or genetic method is the method of Science in general, but considered and employed under a limited aspect. And under its more comprehensive aspect it may be called--though no name is unimpeachable--the method of development. Now the essence of the idea of development--as was clearly shown by Leibniz--is the refusal to admit external interference, and the resolve to let a thing explain itself by itself. It does not, like the mechanical method, manipulate the thing from outside--try to add it up out of factors or items fashioned and fabricated after some external standard. Nor does it, like the chemical, look at the result as an inexplicable alteration, due apparently to a mere stroke of combination or disintegration--yet not obviously reducible to a mere equivalent of its elements. On the contrary, it recognises in the object a certain independence or originality, yet also the presence of an immanent law which does not wait for the outsider to put it together, but constructs itself, as it were, after a plan of its own. There is in the so-called object, though we do not at first sight recognise it, the same originative principle both analytic and synthetic, as we own in thought. The object is--in a true logic--a process, a self-completing process, and not merely an object, mechanical, or other object. It changes, grows or decays, while we observe, unless for brief instants we cut it off from its connexions and arrest its development. And our observation, if truly scientific, must be sympathetic with its process of change. It is neither a mere thing to be explained and construed _ab extra_: nor a mystery of sudden transformation to be passively accepted; but a growth, a history, to be sympathetically watched and understood,--understood, because it follows the same order as the movement of our own thought in the process of knowledge. _Similia similibus cognoscuntur_[6].