Conservation, then, is the common point to which all the energies, all
the powers, all the faculties of beings, seem continually directed.
Natural philosophers call this direction or tendency, SELF-GRAVITATION:
NEWTON calls it INERT FORCE: moralists denominate it in man, SELF-LOVE
which is nothing more than the tendency he has to preserve himself--a
desire of happiness--a love of his own welfare--a wish for pleasure--a
promptitude in seizing on every thing that appears favourable to his
conservation--a marked aversion to all that either disturbs his
happiness, or menaces his existence--primitive sentiments, that are
common to all beings of the human species; which all their faculties are
continually striving to satisfy; which all their passions, their wills,
their actions, have eternally for their object and their end. This self-
gravitation, then, is clearly a necessary disposition in man, and in all
other beings; which, by a variety means, contribute to the preservation
of the existence they have received, as long as nothing deranges the
order of their machine, or its primitive tendency.

Cause always produces effect; there can be no effect without cause.
Impulse is always followed by some motion, more or less sensible; by
some change, more or less remarkable in the body which receives it. But
motion, and its various modes of displaying itself, is, as has been
already shewn, determined by the nature, the essence, the properties,
the combinations of the beings acting. It must, then, be concluded that
motion, or the modes by which beings act, arises from some cause; that
as this cause is not able to move or act, but in conformity with the
manner of its being or its essential properties, it must equally be
concluded, that all the phenomena we perceive are necessary; that every
being in Nature, under the circumstances in which it is placed, and with
the given properties it possesses, cannot act otherwise than it does.