1. Ayers, M. (1997). Is Physical Object a sortal concept? A reply to Xu. Mind and Language, 12, 393–405.
2. Bueno, O. (2014). Why identity is fundamental. American Philosophical Quarterly, 51, 325–332.
3. Campbell, J. (2002). Reference and consciousness. New York: Oxford University Press.
4. Carey, S. (1995). Continuity and discontinuity in cognitive development. In Smith and Osherson (1995).
5. Carey, S., & Xu, F. (1999). Sortal and kinds: An appreciation of John McNamara. In Jackendoff, Bloom and Wynn (1999) (pp. 311–336).