Problem of pluralism
The story is, Descartes was drunk on a summer afternoon and was watching a fly on a wall. It would land, and then fly around, and then land, and then fly around and land. Descartes, being a genius, wondered to his drunk self how he would express the various points where the fly had landed mathematically.
Thus, Cartesian coordinates.
If you think about it, the plurality of possible positions is also the problem that gets Descartes started on epistemology.
He imagines, in the start of Meditations, multiple possible perspectives of reality. He has a 17th century Catholic view, but he can imagine having the view or an "infidel" atheist, an insane person, or a dreaming person.
Whereas, though, in math, multiple possible positions can be quite interesting, quite useful even, with, say, Cartesian points or the calculation of a parallax, ontologically, with a view to ultimate reality, the plurality of possible positions is unsettling.
Each possible alternative view imagined is another possible way to be wrong.
Worse, each possible alternative view proves that the one I hold is also positionally defined. Thus, contingent. It's a result, only, of standing where I stand.
Peter Berger describes this as the crisis of pluralism, where "specific agglomerations of 'reality' and 'knowledge' pertain to specific social contexts," which is the "vertigo of relativity."
It's odd for me to consider epistemological problems as sociological ones, yet Descartes shows that the lack of certainty is closely connected with one's ability to imagine other social positions, and thus realizing one's own contextualization. The epistemological problem of modernism rises out of that lived experience of multiple possible views of reality. And that's a social reality of pluralism, whether Descartes' in the 17th century or evangelicals' 20th and 21st.