This paper looks at how we identify things by comparing the sameness of their characteristics, how we associate symbols with things to simplify identifying them, and concludes there are six aspects that make up an identifier: a thing, a symbol, an association, a context, an agent, and a remembrance. It then considers some of the qualities of identifiers in more detail: scope, uniqueness, granularity, intelligence, actionability, persistence, extensibility, and context. It finally provides a simple checklist for designing identifiers.