Arnold Geulincx (Dutch pronunciation: [ˈɣøːlɪŋks]; 31 January 1624 – November 1669) was a Flemish philosopher. He was one of the followers of René Descartes who tried to work out more detailed versions of a generally Cartesian philosophy. Samuel Beckett cited Geulincx as a key influence and interlocutor because of Geulincx's emphasis on the powerlessness and ignorance of the human condition.
Geulincx was born in Antwerp. He studied at the University of Leuven and was made professor of philosophy there in 1646. He lost his post in 1658, possibly for religious reasons, or (as has been suggested) a combination of unpopular views and his marriage in that year. Geulincx then moved north to the University of Leiden and converted to Calvinism. Initially he gave private lessons. He was appointed reader in logic there in 1662 and extraordinary professor in 1665. He died in Leiden in 1669, leaving most of his works, all written in Latin, to be published after his death. They were edited by Cornelis Bontekoe.
Despite Geulincx's thesis that God cannot act without an instrumentality of variety, he was strongly attacked in the early eighteenth century, for example by Ruardus Andala and Carolus Tuinman, as a Spinozist. This criticism had originated from Christian Thomasius in 1710. The attack from Andala was on behalf of the 'true' Cartesians, classing Geulincx as pernicious, with Burchardus de Volder, Jean LeClerc, Frederik van Leenhof, Pontiaan van Hattem and Willem Deurhoff. Geulincx was also attacked by the Pietist Joachim Lange, as part of a campaign against Christian Wolff; and regarded with Pierre Bayle as insidiously anti-Christian by Johann Franz Buddeus.