Abstract: There is no description of modernity without functional differentiation. The distinction of function systems such as economy, science, art, or religion, is a key to modernity. Modern science, however, applies and implies rather than studies functional differentiation without providing exact definitions of function systems or investigating how many of these systems actually exist. The present article addresses these two issues focusing on the second. Test criteria for the distinction between function systems and systems other than function systems are developed and used to decide whether family, love, morality, culture, social work, and some more, actually are function systems. Subsequently, the article presents a list of 10 function systems and their corresponding media, codes, and programs. A final section suggests that a disciplined approach to functional differentiation opens up a horizon for interfunctional comparative social research.

Keywords: Functional differentiation; function system; social systems; form theory; Niklas Luhmann; modernity; interfunctional comparative social research.