Boysen, S. and Berntson, G. 1989: "Numerical Competence in a Chimpanzee (Pan Troglodytes)". Journal of Comparative Psychology, 103, pp. 23-31.
Capaldi, E. and Miller, D. 1989: "Counting in Rats: Its Functional Significance and the Independent Cognitive Processes Which Comprise It". Journal of Experimental Psychology: Animal Behaviour Processes, 14, pp. 3-1 7.
Church, R. and Meck, W. 1984: "The Numerical Attribute of Stimuli", in H. Roitblatt, T. Bever, and H. Terrace (eds.) Animal Cognition. Hillsdale, NJ: Erlbaum.
Crossley, J. 1980: The Emergence of Number. Victoria, Australia: Upside Down Book Co.
Giaquinto, M. 1995: "Concepts and Calculation". Mathematical Cognition, pp. 6 1-8 1.
Gray, J. 1979: Ideas of Space. Oxford: Oxford University Press.
Leslie, A. 1988: "The Necessity of Illusion: Perception and Thought in Infancy", in Weiskrantz, (ed.) Thought Without Language. Oxford: Oxford University Press.
Peacocke, C. 1992: A Study of Concepts. Cambridge, Mass: MIT Press.
-1993: "How Are A Priori Truths Possible?". European Journal of Philosophy 1, pp. 175-99.
Putnam, H. 1962: "The Analytic and the Synthetic", reprinted in H. Putnam Mind, Language and Reality: Philosophical Papers, Volume 2. Cambridge: Cambridge University Press, 1975. Originally published in Feigl, H. and Maxwell, G. (eds.) Minnesota Studies in the Philosophy of Science, 111. Minneapolis: University of Minnesota Press.