 Philosophical realists view the emergence of objects from the stuff as an objective matter independent of human thought or interests; conceptualist  philosophers argue instead that it is human cognition (and nominalist that it is language as well) that produces the appearance of objects. Many philosophers have believed that the notion of a sortal is a, perhaps the, crucial philosophical tool in analyzing these issues and resolving the debates. Recently psychologists have also taken notice of the concept and argued for the importance of sortals in cognitive development. And researchers in artificial intelligence, specifically knowledge representation, have also started to use the idea. Unfortunately, there are conflicting understandings of the technical philosophical term sortal; authors often write at cross-purposes, which means that readers of any text about sortals should approach cautiously. 