 Rheinberger refers to theoretical entities as “epistemic things”. This concept signifies the “material entities or processes—physical structures, chemical reactions, biological functions—that constitute the objects of inquiry” (Rheinberger 1997, 28). Epistemic things can unexpectedly appear and disappear, or be re-constituted in new guises as experimental systems are developed. Sufficiently stabilized epistemic things can “turn into the technical repertoire of the experimental arrangement” (1997, 29) and thus become “technical objects.” One of Rheinberger’s examples of an epistemic thing is the ribosome (a comparatively large molecular complex of protein and RNA that catalyzes some of the crucial steps in protein synthesis). Here, it can be argued that whether or not some experimental setup contained ribosomes is a theoretical judgment. Thus, an experimental system contains materials and apparatus as well as observation concepts and theoretical concepts. They are rather heterogeneous ontologically.