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A taxonomic class is a taxonomic rank conventionally below a taxonomic phylum and above a taxonomic order. A particular class is a taxon at that level. For example, Mammalia is the class of mammals, and Carnivora is one of its constituent orders.^[ref]

The hierarchy makes several statements simultaneously: an individual cat belongs to Mammalia, Carnivora and Felidae, at class, order and family ranks respectively. These nested memberships describe increasing specificity. They do not give three independent estimates of the cat's identity.

Consider a constructed sampling table with two classes, each represented by twelve sampled species. The first has two sampled orders containing six species each; the second has three containing four each. The class totals agree, while the within-class distribution differs. Class-level aggregation preserves the total and discards that structure. Nor would twelve sampled species establish twelve species in the complete class: sampling coverage is a separate issue.

A taxonomic class need not have a fixed number of orders, individuals or species. Its rank also does not specify a fixed age or a numerical amount of genetic divergence. Those are additional biological quantities or hypotheses that require evidence beyond the hierarchical label.

A taxonomic kingdom is a major taxonomic rank conventionally below a domain and above a taxonomic phylum. A kingdom is a particular taxon at that rank, while the rank word identifies its place in a classification. In a familiar classification of eukaryotes, animals and plants belong to different kingdoms within the same domain.^[ref]

Nested membership permits several descriptions of one organism. An individual animal can belong to the eukaryotic domain, the animal kingdom and a particular phylum simultaneously. The levels select different scales of grouping, rather than offering competing identifications.

A constructed classification database illustrates the information supplied by parent relationships. Suppose kingdom A contains phyla P and Q, with 8 and 12 recorded species, while kingdom B contains phylum R with 20 recorded species. Both kingdom totals are twenty, but A's records are divided between two phyla and B's are not. A query grouped only by kingdom loses that distribution. The counts describe the stipulated records, not a census of complete biological diversity.

The kingdom rank does not prescribe a fixed number of phyla or a particular evolutionary age. Nor does sharing that rank establish equal evolutionary distance between any two groups. A phylogenetic tree represents hypotheses about ancestry and branching; a ranked classification assigns names to selected groupings.^[ref] Keeping the rank, the membership and the supporting evidence separate makes comparisons across classifications more interpretable.

A taxonomic phylum is a major taxonomic rank conventionally below a taxonomic kingdom and above a taxonomic class. A particular phylum is a taxon at that rank. For example, chordates form the phylum containing Mammalia, which in turn contains orders such as Carnivora.^[ref]

The same animal can consequently belong to a phylum, a class and an order without these being competing identifications. Each level adds information about nested membership. The rank word phylum identifies a position in the hierarchy; the group name identifies which taxon occupies that position.

For a constructed survey example, suppose one phylum is represented by four sampled classes with 3, 7, 2 and 8 sampled species. Its total is $3+7+2+8=20$. A second phylum with two sampled classes containing ten species each has the same total. Reporting only twenty species for each phylum loses the class-level distribution, and neither count establishes the total diversity of the unsampled phylum.

A taxonomic rank does not itself specify a fixed age, number of constituent groups or numerical genetic distance. A phylogenetic tree addresses evolutionary relationships, while ranked names select particular groupings for classification.^[ref] The usefulness of the rank comes from organizing comparisons; the scientific interpretation still depends on what was sampled and the evidence supporting membership.