Some scruple of conscience forbade him to proceed to the priesthood, and he remained throughout life a "clerk in minor orders," although a profound theological scholar.

For some years he was a master in the "little school" for boys established at Port Royal, and had the honour of teaching Greek to young Jean Racine, the future poet.

But his chief duty was to act, in collaboration with Antoine Arnauld, as general editor of the controversial literature put forth by the Jansenists.

In 1664 he himself began a series of letters, Les Imaginaires, intended to show that the heretical opinions commonly ascribed to the Jansenists really existed only in the imagination of the Jesuits.

This remark stung Racine to the quick; he turned not only on his old master, but on all Port Royal, in a scathing reply, which—as Boileau told him—did more honour to his head than to his heart.

But Nicole's most popular production was his Essais de morale, a series of short discussions on practical Christianity.