This end they attained by steps which can not well be related here,
but which led them to suppose separate powers behind each of the
natural series--powers having no relation to the qualities of mankind,
but ever acting to a definite end. Thus Plato, who represents most
clearly this advance in the interpretation of facts, imagined that
each particular kind of plant or animal had its shape inevitably
determined by something which he termed an idea, a shape-giving power
which existed before the object was created, and which would remain
after it had been destroyed, ever ready again to bring matter to the
particular form. From this stage of understanding it was but a short
step to the modern view of natural law. This last important advance
was made by the great philosopher Aristotle, who, though he died about
twenty-two hundred years ago, deserves to be accounted the first and
in many ways the greatest of the ancient men of science who were
informed with the modern spirit.

With Aristotle, as with all his intellectual successors, the
operations of Nature were conceived as to be accounted for by the
action of forces which we commonly designate as natural laws, of which
perhaps the most familiar and universal is that of gravitation, which
impels all bodies to move toward each other with a degree of intensity
which is measured by their weight and the distance by which they are
separated.

For many centuries students used the term law in somewhat the same way
as the more philosophical believers in polytheism spoke of their gods,
or as Plato of the ideas which he conceived to control Nature. We see
by this instance how hard it is to get rid of old ways of thinking.
Even when the new have been adopted we very often find that something
of the ancient and discarded notions cling in our phrases. The more