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 winds, when the waves roll high as mountains, there is not a single particle of dust, or drop of water, that has been placed by CHANCE, that has not a cause for occupying the place where it is found; that does not, in the most rigorous sense of the word, act after the manner in which it ought to act; that is, according to its own peculiar essence, and that of the beings from whom it receives this communicated force. A geometrician exactly knew the different energies acting in each case, with the properties of the particles moved, could demonstrate that after the causes given, each particle acted precisely as it ought to act, and that it could not have acted otherwise than it did.