eing we can form no idea); compound, if it is formed of
different elements, which have each their proper situation, and have a
natural tendency to it--this element tending towards the highest parts,
that towards the lowest, and another towards the middle. This
conjunction may for some time subsist, but not forever; for every
element must return to its first situation. No animal, therefore, is
eternal.

But your school, Balbus, allows fire only to be the sole active
principle; an opinion which I believe you derive from Heraclitus, whom
some men understand in one sense, some in another: but since he seems
unwilling to be understood, we will pass him by. You Stoics, then, say
that fire is the universal principle of all things; that all living
bodies cease to live on the extinction of that heat; and that
throughout all nature whatever is sensible of that heat lives and
flourishes. Now, I cannot conceive that bodies should perish for want
of heat, rather than for want of moisture or air, especially as they
even die through excess of heat; so that the life of animals does not
depend more on fire than on the other elements.

However, air and water have this quality in common with fire and heat.
But let us see to what this tends. If I am not mistaken, you believe
that in all nature there is nothing but fire, which is self-animated.
Why fire rather than air, of which the life of animals consists, and
which is called from thence _anima_,[248] the soul? But how is it that
you take it for granted that life is nothing but fire? It seems more
probable that it is a compound of fire and air. But if fire is
self-animated, unmixed with any other element, it must be sensitive,
because it renders our bodies sensitive; and the same objection which I
just now made will arise, that whatever is sensitive must necessarily
be susceptible of pleasure and pain, and whatever is sensible of pain
is likewise subject to the approach of death; therefore you cannot
prove fire to be eternal.

You Stoics hold that all fire has need of nourishment, without which it
cannot possibly subsist; that the sun, moon, and all the stars are fed
either with fresh or salt waters; and the reason that Cleanthes gives
why the sun is retrograde, and does not go beyond the tropics in the
summer or winter, is that he may not be too far from his sustenance.
This I shall fully examine hereafter; but at present we may conclude
that whatever may cease to be cannot of its own