Rene Descartes (1596–1650), the great philosopher-mathematician from Touraine, France, was Catholic and Jesuit-trained. Like Comenius, he was a realist, but he never integrated the spiritual and the natural; thus he developed his dualistic philosophy. He is generally the first modern rationalist thinker.

In 1642, Descartes met Comenius at Endegeest near Leyden, Holland. The meeting was arranged by Samuel Hartlib, a mutual friend. Comenius was by this time a renowned educationist, Descartes was already a celebrity for his new philosophy. They met, cordially, for four hours, discussing their respective views of reality.

The two were not on the same wavelength. The fact that Descartes was Catholic and Comenius Protestant is not insignificant, but should not be overplayed. It was a conflict of mindsets. Descartes had little use for Comenius’s efforts to integrate spiritual realities with the discoveries of science, nor for his dedication to the pansophic ideal of a unified knowledge, nor for his proposal for a universal language.

Comenius, on the other hand, found Descartes’s rejection of Biblical authority in the natural sciences quite disturbing. Descartes’s use of doubt to arrive at truth and his intellectual arguments for the existence of God were simply foreign to Comenius’s way of thinking.

Later, Comenius was to write scathing critiques of Cartesian philosophy. In these, he further showed the great gulf fixed between his own Christian humanism and Descartes’s rationalism. It is apparent that Comenius never really understood Descartes’s analytical geometry nor his contributions to mechanical physics. What he did understand was that Cartesian philosophy was a clear threat to the unity of knowledge Comenius was striving for in his pansophism, which incorporated spiritual elements with scientific evidence.

Both Descartes and Comenius lived in free-thinking Holland for a time. They also both had significant interactions with Sweden. Earlier, Comenius had been hired to reform the Swedish school system. Later, Descartes was invited to tutor Queen Christina. It is said that Christina developed an aversion to Comenius and refused to study from any of his books. Later in life, possibly through Descartes’s influence, she converted to Catholicism, abdicating her throne.