Nothing can be destroyed, except by a cause external
to itself.Proof.--This proposition is self--evident, for the definition
of anything affirms the essence of that thing, but does not
negative it; in other words, it postulates the essence of the
thing, but does not take it away. So long therefore as we regard
only the thing itself, without taking into account external
causes, we shall not be able to find in it anything which could
destroy it. Q.E.D.