A study with nonhuman primates

Philosophers and psychologists of language have coined the term "sortal" to refer to the concepts which underpin count nouns. A sortal is a concept which provides criteria for individuation and numerical identity. Criteria for individuation are the basis for counting; we cannot count without specifying a count noun such as "cat" or "table". Criteria for numerical identity (in the sense of one and the same one) are the basis for tracking individuals through time and space; we cannot ask questions about numerical identity without a count noun, e.g., "the same cat" or "the same table". Recent research has begun to address the question whether pre-linguistic infants represent sortal concepts (Spelke, Kestenbaum, Simons, & Wein, 1995; Xu & Carey, 1996).