repudiation of the mechanical
hypothesis that all quality is founded upon quantity, or upon
composition and decomposition. Quality has a real existence of its
own. He rejects, also, the view that space is a physical thing. If
this were true, there would be two bodies occupying the same place at
the same time, namely the object and the space it fills. Hence there
is nothing for it but to conceive space as limit. Space is, therefore,
defined as the limit of the surrounding body towards what is
surrounded. As we shall see later, in another connexion, Aristotle did
not regard space as infinite.

Time is defined as the measure of motion in regard to what is earlier
and later. It thus depends for its existence upon motion. If there
were no change in the universe, there would be no time. And since it
is the measuring or counting of motion, it also depends for its
existence upon a counting mind. If there were no mind to count, there
could be no time. This presents difficulties to us, if we conceive
that there was a time when conscious beings did not exist. But this
difficulty is non-existent for Aristotle, who believed that men and
animals have existed from all eternity. The essentials of time,
therefore, are two: change and consciousness. Time is the succession
of thoughts. If we object that the definition is bad because
succession already involves time, there is doubtless no answer
possible.

As to the infinite divisibility of space and time, and the riddles
proposed thereupon by Zeno, Aristotle is of opinion that space and
time are potentially divisible {293} _ad infinitum_, but are not
actually so divided. There is nothing to prevent us from going on for
ever with the process of division, but space and time are not given in
experience as infinitely divided.

After these preliminaries, we can pass on to consider the main subject
of physics, the scale of being. We should notice, in the first place,
that it is also a scale of values. What is higher in the scale of
being is of more worth, because the principle of form is more advanced
in it. It constitutes also a theory of development, a philosophy of
evolution. The lower develops into the higher. It does not, however,
so develop in time. That the lower form passes in due time into a
higher form is a discovery of modern times. Such a conception was
impossible for Aristotle. For him, genus and species are eternal. They
have neither beginning nor end. Individual men are born