A valid name is the correct name for a taxon, i.e. the oldest potentially valid name of a name bearing type that falls with an author’s concept of the taxon (Chapter 6). “Potentially valid” means the name must be available, but not otherwise invalid for any other reason, such as being a junior homonym.
- The “principle of priority” is the principle that the valid name of a taxon is the oldest potentially valid name (Article 23). The purpose of this is to promote the stability of names.
- When two taxa are synonymised the valid name is determined by the principle of priority (Article 23.3).
- Similarly when two taxa are homonyms the valid name is determined by the principle of priority (Article 23.4, 52, Chapter 12).
- When two synonyms or homonyms are published at the same time the valid name is determined automatically if one is at higher rank (24.1) or by decision of the first reviser (24.2).
- The order of names within a work is not relevant – “page priority” is not generally recognized by the Code.
Sometimes what is valid can be a subjective judgment. E.g. if one taxonomist considers two names belong to one species, then he will treat the junior name as an invalid synonym, however if another taxonomist considers the names belong to different species, she will treat the junior name as valid. It is the task of the taxonomist and not the Commission to judge such subjective matters of taxonomic practice, however once decided the Code should allow the valid name(s) to be determined.