Arnold (or Arnout) Geulincx was baptized in Antwerp in late January 1624. He reportedly spoke Latin fluently even as a child, matriculated at Leuven University in January 1640, and became professor primarius there in 1652. Six years later, he seems to have made the decision to move to Leiden because he intended to marry his niece Susanna Strickers, a step his Leuven career as canon and professor prohibited.

It was in Leiden that Geulincx became a Cartesian. Apart from the idea of mind-body dualism, his Cartesianism was inspired by the notion of epistemological growth found in the paragraphs on childhood prejudice in Descartes’ Principles of Philosophy. Yet Geulincx also went beyond Descartes. Instead of dealing only with sensations, he developed a parallel notion of conceptual projections on reality, arguing that it is on the basis of our “ways of thinking” (modi cogitandi) that we misrepresent things “as they are in themselves.” This may well be seen as a prefiguration of Kant, as long as it is kept in mind that Geulincx was not thinking in terms of necessary categories, but rather of epistemological distortions – the misrepresentations of reality consolidated in the concepts of Aristotelian metaphysics. According to Geulincx (1891–93, 2:301), to regard things in themselves as substances (or even as “things”) was simply a way of applying intellectual phasmata to the outside world alongside our phasmata of sense. Wisdom, on the other hand, results from the fact that “something divine within us” tells us that “it is not so.”

Geulincx's epistemology has been read in terms of both an illumination theory (Vleeschauwer 1953) and a theory of vision in God (Aalderink 2009). Against this, it must be said that Geulincx never explicitly discussed the question “where” our ideas originate. Indeed, unlike Augustine and Malebranche, but very much like Descartes himself, Geulincx conceived the dissimilarity between sensual information and its intellectual reinterpretation in such a way that there was no need to address the Platonic question as to how ideas might represent objects (see representation).