To construct them we have to look at experience, to be realistic, to search within experience to find knowledge, to take the proper perspective and see the common elements. The distinction between artifacts in singular and plural periods is simply whether we construct entities based on difference or on sameness. Here we complete the logic of unique artifacts and find all of the forms of the elements of knowledge. When we look at all languages we again find a variety of common ways to specify such collections or categories. We distinguish common nouns, proper nouns, and mass nouns.
Proper nouns are entities for they name single thing.
Common nouns are generally sites for they name collections. And mass nouns, too, are always sites, representing collections. Adjectives specify not only a member of a class but clarify that the noun itself represents a collection. Sites are the classes and categories of our knowledge. Like noun phrases they come in two types - parts and wholes, splitting each entity period into two distinct halves.