Jansen, Cornelius (1585-1638), a celebrated Dutch theologian, was born near Gorcum in Holland of humble parentage. He studied at the University of Louvain, first at the Jesuit's college, and afterwards at the college of Adrian IV., where he fell under the influence of Jacobus Jansonius, from whom he imbibed the Augustinian doctrine of grace. In 1604 he went to Paris, and afterwards spent several years with Vergerius at Bayonne. In 1617 he was summoned to Louvain to take the headship of the new college of St. Pulcheria. In 1619 he took the degree of doctor in theology, and in 1630 became professor of Biblical exegesis. All this time he was actively using his influence against the Jesuits, and as the result of two visits he made to Spain in 1624 and 1626, certain encroachments made by them on the privileges of Louvain University were restrained. In 1636 he was made bishop of Ypres, as a reward for a work published by him under a pseudonym against the alliance of France with the Protestant Gustavus Adolphus.
For the last twenty-two years of his life he was at work upon his great treatise "Augustinus, seu doctrina S. Augustini de humanae naturae Sanitate, aegritudine, et medicina, adversus Pelagianos et Massilienses," which was published, posthumously, in 1640 in three folio volumes. The importance of the work lay in the epilogue, in which the doctrines of the Jesuits were compared to the errors of the Massilians.
In France the matter later became an important political question. After a struggle, the bull called "Unigenitus" (1713) was registered as a law by the Parliament of Paris. After this the Jansenists in France declined into a set of mystical fanatics. [Paris, Francois de.]