  I would very much like to thank my collaborators at the University of Cologne Anna Pavani, Manuel Lorenz, Ina Schall, Fedora Hartmann, Emil Gaub and especially Laura Marongiu. I would also like to thank the anonymous referee for most useful remarks and corrections. Thanks are due to the fantastic team of the Stanford Encyclopedia of Philosophy and its principal editor Edward N. Zalta for their patience and detailed observations. Last but not least let me thank Merrie Bergmann for correcting the English and many useful suggestions.  