We often say that things differ in degree but not in kind, as though
there were a fixed line at which degree ends and kind begins. There is
no such line. All differences resolve themselves into differences of
degree. Everything can in the end be united with everything by easy
stages if a way long enough and round-about enough be taken. Hence to
the metaphysician everything will become one, being united with
everything else by degrees so subtle that there is no escape from seeing
the universe as a single whole. This in theory; but in practice it would
get us into such a mess that we had better go on talking about
differences of kind as well as of degree.