Hair, J.F. et al. (1992). Multivariate data analysis (3rd ed.). New York: Macmillan - Explains a consistent treatment of objects and their properties. (see also http://www.socialresearchmethods.net/tutorial/Flynn/refer.htm) 

 * Introduction to Object Oriented Programming (OOP) concepts, http://www.codeproject.com/KB/architecture/OOP_Concepts_and_manymore.aspx. - Provides a good entrance to understanding of a consistent treatment of reality in terms of objects, like the Linnean classification.   

 * Basic Concepts of Mathematics, by Elias Zakon, ISBN 1-931705-00-3 -Gives a good entrance to understanding of mathematics. May make cladists understand why 1+1=2 (and not 1).