Flemish metaphysician, logician, and leading exponent of a philosophical doctrine known as occasionalism based on the work of René Descartes, as extended to include a comprehensive ethical theory.

Geulincx studied philosophy and theology at the Catholic University of Leuven (Louvain), where he became a professor in 1646. In 1658 he was dismissed, probably because of his sympathy with Jansenism, the Roman Catholic movement emphasizing man's sinful nature and dependency on God's grace for salvation. Taking refuge at Leiden, in Holland, he adopted the strict, Jansen-like theology of John Calvin. In September 1658 he became a medical doctor and, in the following year, was authorized to lecture privately in philosophy for a few months. He lived in poverty until 1662, when he obtained a lectureship in logic at the University of Leiden, where in 1665 he became professor extraordinary of philosophy and ethics.

Geulincx's major works include Quaestiones Quodlibeticae (1653; “Miscellaneous Questions”), reedited by him at Leiden as Saturnalia (1665); Logica . . . Restituta (1662; “Logic Restated”); and the ethical dissertation De Virtute (1665; “On Virtute”). After his death, his pupil C. Bontekoe published, under Geulincx's pseudonym, Philaretus, his six treatises on ethics, Gnothi Seauton (1675; “Know Thyself ”). As Philaretus, Geulincx accepted the progression in Cartesian metaphysics from doubt to knowledge and from knowledge to God and affirmed the dominant role of the will in forming judgments. Geulincx, however, aimed to submit the will to the authority of reason. This “ethics of humility” reflects the author's Jansenism and Calvinism. In his Metaphysica Vera (1691; “True Metaphysics”), he disappointed Cartesian expectations that a scientific mastery of matter, life, and mind will develop and instead emphasized man's impotence before the transcendent Creator.

The inspiration for Geulincx's attempt to complete Descartes's system came primarily from the writings of St. Augustine. The opposition between the incomprehensible Deity and his creation also formed the basis for Geulincx's doctrine of occasionalism: God uses the “occasion” of the body to produce various human attitudes. Though people may believe that they act unaided, God actually works within them to make their will effective.

Geulincx's works have been collected as Arnoldi Geulinex Antverpiensis Opera Philosophica, 3 vol. (1891–93; “The Philosophical Works of Arnold Geulincx of Antwerp”).