Necessity is the constant and infallible relation of causes with their
effects. Fire consumes, of necessity, combustible matter plated within
its circuit of action: man, by fatality, desires either that which
really is, or appears to be serviceable to his welfare. Nature, in all
the extraordinary appearances she exhibits, necessarily acts after her
own peculiar essence: all the beings she contains, necessarily act each
after its own a individual nature: it is by motion that the whole has
relation with its parts; and these parts with the whole: it is thus that
in the general system every thing is connected: it is itself but an
immense chain of causes and effects, which flow without ceasing, one
from the other. If we reflect, we shall be obliged to acknowledge that
every thing we see is necessary; that it cannot be otherwise than it is;
that all the beings we behold, as well as those which escape our sight,
act by invariable laws. According to these laws, heavy bodies fall--
light bodies ascend--analogous substances attract each other--beings
tend to preserve themselves--man cherishes himself; loves that which he
thinks advantageous--detests that which he has an idea may prove
unfavourable to him.--In fine, we are obliged to admit, there can be no
perfectly independent energy--no separated cause--no detached action, in
a nature where all the beings are in a reciprocity of action--who,
without interruption, mutually impel and resist each other--who is
herself nothing more than an eternal circle of motion, given and
received according to necessary laws; which under the same given
incidents, invariably produce the same effect.

Two examples will serve to throw the principle here laid down, into
light--one shall be taken from physics, the other from morals.

In a whirlwind of dust, raised by elemental force, confused as it
appears to our eyes, in the most frightful tempest excited by contrary