Roughly speaking, “opaque ignorance” is a kind of ignorance in which one is not even aware of one’s ignorance. It has already been observed by some authors that there are different kinds of opaque ignorance, among them the particularly interesting case of “deeply opaque ignorance.” This paper, explores this kind of ignorance by relating it to the concept of incommensurability, more specifically to “strong incommensurability”, a new concept. Does strong incommensurability imply deeply opaque ignorance? Hoyningen-Huene will discuss this question both on an abstract level and by means of several cases studies from the history of science and the history of
medicine (Mercury’s perihelion, viruses, prions).