Geulincx summarized his philosophy in the phrase, "Ita est, ergo ita sit", ("it exists, therefore it is so"). He believed in a "pre-established harmony" as a solution to the mind-body problem, dying 25 years before Leibniz's better–remembered formulation of the idea. In Leibniz's philosophy, the doctrine of pre-established harmony was linked with optimism, the notion of this world as the "best of all possible worlds". But Geulincx made no such linkage.
He is cited by Samuel Beckett, whose character Murphy remembers the 'beautiful Belgo-Latin of Arnold Geulincx', and in particular the gloomy nostrum (frequently repeated by Beckett to inquisitive critics) Ubi nihil vales, ibi nihil velis (roughly, 'Where you are worth nothing, there you should want nothing.') Beckett's character Molloy describes himself as "I who had loved the image of old Geulincx, dead young, who left me free, on the black boat of Ulysses, to crawl towards the East, along the deck".