A language does not become fixed.

The human intellect is always on the march, or, if you prefer, in movement, and languages with it.

Things are made so.

When the body changes, how could the coat not change?
The French of the nineteenth century can no more be the French of the eighteenth, than that is the French of the seventeenth, or than the French of the seventeenth is that of the sixteenth.

Montaigne's language is not Rabelais's, Pascal's is not Montaigne's, Montesquieu's is not Pascal's.