When we speak of Cartesianism we do not mean the metaphysical system of the master, or any of his particular views such as that of innate ideas.  We mean the general principles, which were to leave an abiding impression on the texture of thought:  the supremacy of reason over authority, the stability of the laws of Nature, rigorous standards of proof.  Fontenelle was far from accepting all the views of Descartes, whom he does not scruple to criticise; but he was a true Cartesian in the sense that he was deeply imbued with these principles, which generated, to use an expression of his own, “des especes de rebelles, qui conspiraient contre l’ignorance et les prejuges dominants.” [Footnote:  Eloge de M. Lemery.] And of all these rebels against ruling prejudices he probably did more than any single man to exhibit the consequences of the Cartesian ideas and drive them home.

The Plurality of Worlds was a contribution to the task of transforming thought and abolishing ancient error; but the History of Oracles which appeared in the following year was more characteristic.  It was a free adaptation of an unreadable Latin treatise by a Dutchman, which in Fontenelle’s skilful hands becomes a vehicle for applying Cartesian solvents to theological authority.  The thesis is that the Greek oracles were a sacerdotal imposture, and not, as ecclesiastical tradition said, the work of evil spirits, who were stricken silent at the death of Jesus Christ.  The effect was to discredit the authority of the early Fathers of the Church, though the writer has the discretion to repudiate such an intention.  For the publication was risky; and twenty years later a Jesuit Father wrote a treatise to confute it, and exposed the secret poison, with consequences which might have been disastrous for Fontenelle if he had not had powerful friends among the Jesuits themselves.  Fontenelle had none of the impetuosity of Voltaire, and after the publication of the History of Oracles he confined his criticism of tradition to the field of science.  He was convinced that “les choses fort etablies ne peuvent etre attaquees que par degrez.” [Footnote:  Eloge de M. Lemery.]

The secret poison, of which Fontenelle prepared this remarkable dose with a touch which reminds us of Voltaire, was being administered in the same Cartesian period, and with similar precautions, by Bayle.  Like Fontenelle, this great sceptic, “the father of modern incredulity” as he was called by Joseph de Maistre, stood between the two centuries and belonged to both.  Like Fontenelle, he took a gloomy view of humanity; he had no faith in that goodness of human nature which was to be a characteristic dogma of the age of illumination.  But he was untouched by the discoveries of science; he took no interest in Galileo or Newton; and while the most important work of Fontenelle was the interpretation of the positive advances of knowledge, Bayle’s was entirely subversive.