Who knows whether the modern age may not prove the exception to the law which has hitherto prevailed?
Let us act as if it would.
This is the practical moral that Le Roy enforces in the last book of his dissertation.

We must not allow ourselves to be paralysed or dismayed by the destinies of past civilisations, but must work hard to transmit to posterity all that has been achieved, and augment the discoveries of the past by new researches.

For knowledge is inexhaustible.

"Let us not be so simple as to believe that the ancients have known and said everything and left nothing to their successors.

Or that nature gave them all her favours in order to remain sterile ever after." Here Le Roy lays down Bodin's principle which was to be asserted more urgently in the following century--the permanence of natural forces.