ABSTRACT
This chapter explores some of the main metaphysical issues that pertain to identity and sameness as they were addressed in the medieval period. To the modern ear, “numerical sameness” might suggest a relation that behaves like identity— that is reflexive, symmetric, transitive, and obeys the principle of the Indiscernibility of Identicals. While the word identitas does appear in medieval philosophical and theological works, it is much more illuminating to say that medieval philosophers developed complicated theories of kinds of sameness and their properties. It should be apparent that medieval thinking about sameness and difference is in several respects markedly different from mainstream contemporary thinking about identity. It is notable that for many medievals, numerical sameness did not necessarily conform to the principle of the Indiscernibility of Identicals. The primary sources for Aristotle’s views on sameness and difference are his Topics, his Physics, and his Metaphysics.
