theologian whose work powerfully influenced Cornelius Jansen (Jansen, Cornelius Otto), one of the fathers of Jansenism.

Baius was educated at the Catholic University of Leuven (Louvain), where he studied philosophy and theology and held various university appointments. In about 1550, with the theologian Jan Hessels, he began to advance revolutionary doctrines of grace and justification based on a new, rigid, and pessimistic interpretation of the writings of St. Augustine (Augustine, Saint). Baius' numerous short treatises on theological subjects incurred censures by ecclesiastical authorities; in 1567, Pope Pius V condemned 79 statements from his works in the bull Ex Omnibus Afflictionibus. Baius submitted, but indiscreet utterances by him and his supporters led to a new condemnation in 1580 by Pope Gregory XIII. Baius, however, kept his professorship and became chancellor of Leuven in 1575.

The most distinctive features of Baius' system, which are found also in some Protestant writers, concern the Fall of man. Baius held that the innocence of Adam and Eve was part of their nature, so that the first sin destroyed intrinsic principles of human nature. His principal works were published by the Maurists in Cologne in 1696, edited by G. Gerberon.