Sandkühler, Hans Jörg (2010). "Ontologie: 4 Aktuelle Debatten und Gesamtentwürfe". Enzyklopädie Philosophie. Meiner. Archived from the original on 2021-03-11. Retrieved 2021-01-27.
Forrest, Peter (Fall 2008). "The Identity of Indiscernibles". In Edward N. Zalta (ed.). The Stanford Encyclopedia of Philosophy. Retrieved 2012-04-12.
Noonan, Harold; Curtis, Ben (2018). "Identity". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Retrieved 4 January 2021.
Marshall, Dan; Weatherson, Brian (2018). "Intrinsic vs. Extrinsic Properties". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Retrieved 25 January 2021.
Sandkühler, Hans Jörg (2010). "Ontologie: 4 Aktuelle Debatten und Gesamtentwürfe". Enzyklopädie Philosophie. Meiner. Archived from the original on 2021-03-11. Retrieved 2021-01-27.
Alfred North Whitehead and Bertrand Russell (1910). Principia Mathematica. Vol. 1. Cambridge: University Press. Here: Sect.13 Identity, Def. 13.01, Lem.13.16.,17., p.176,178