The groups of organisms or species considered potential recipients of scientific names are called taxa. The only taxa whose names are governed by this code are clades. However, species, whose names are governed by the rank-based codes, are frequently used to define clade names in this code. The system of nomenclature described in this code is independent of categorical rank. Although clades are hierarchically related, and therefore intrinsically ranked in the sense that some are more inclusive than others, assignment of categorical ranks is not part of the formal naming process and has no bearing on the spelling or application of clade names. The concepts of synonymy, homonymy, and precedence adopted in this code are, in contrast to the rank-based codes, independent of categorical rank.