An opponent of the Jesuits, Jansen proposed a return to the principles laid down in the work of St Augustine of Hippo. His posthumously published work, Augustinus (1640), gained an increased following, and prominent adherents of Jansenism included Racine and Pascal. In France, Jansenism was associated with the convent of Port-Royal, which operated a number of famous schools that educated Racine and Pascal.
Jansenism emphasized original sin, human depravity, the necessity of divine grace, and predestination. In Jansenist thought, human beings were born bad, and without divine help a human being could never become good. This meant that one had to be very careful about one's choices, exhibit a high level of piety and moral rectitude, and prepare carefully through prayer and confession before receiving Communion (hence they favored less frequent reception). The Jansenist idea of predestination, based on Augustine's writing and close to that of Calvinism, was that only a small number of human beings, the "elect", were destined to be saved.
Jansenism was condemned as heretical in several papal bulls, notably by Innocent X and Clement XI. It is interesting to note that because Jansen himself died before his work was published and he included statements of submission to the Roman church in it, he himself was never considered a heretic. The final condemnation of Jansenism was by St. Pius X, who advocated daily communion and communion for children as soon as they could distinguish the host.