Cultural categories involve different kinds of hierarchies.
One of these is the part-whole hierarchy. On the other hand, a taxonomic hierarchy identifies an item as a member of a class of classes of items. An animal is a whole kind of thing. The grammatical hierarchy deals with conversational structure, with monologues broken into paragraphs, with sentences broken into clauses, with phrases broken into words, and with sequences of morphemes broken into single morphemes. The word boys, for example, is broken into the two morphemes boy and s. Grammatical structuring involves such units, in some kind of sequence.