1. Armstrong, D. (1978). Universals and scientific realism I: Nominalism and realism. Cambridge University Press.
2. Armstrong, D. (2005). Four disputes about properties. Synthese, 144, 309–320.
3. Bacon, J. (1995). Universals and property instances: The alphabet of being. Blackwell.
4. Black, M. (1952). The identity of indiscernibles. Mind, 61, 153–164.
5. Brownstein, D. (1973). Aspects of the problem of universals, humanistic studies (p. 44). University of Kansas Publications.