After this is done, Goodman faces his second major constructional objective. He has to order the qualia into different categories. The problem is to construct for each of the categories (color, time, place, and so forth) a map that assigns a unique position to each quale in the category, and that represents the relative likeness of qualia by nearness in position. The solution to the problem requires in each case the specification of a set of terms by means of which the order at hand can be described, and then the selection of primitives suitable to define them. Goodman thereby shows how predicates referring to size and shape of phenomenal concreta may be introduced, and he suggests briefly some approaches to the definition of the different categories of qualia by reference to their structural characteristics.