In zoological nomenclature, the valid name of a taxon is the zoological name that is to be used for that taxon following the rules in the International Code of Zoological Nomenclature (ICZN). In other words: a valid name is the correct zoological name of a taxon.
In contrast, an invalid name is a name that violates the rules of the ICZN. An invalid name is not considered to be a correct scientific name for a taxon. Invalid names may be divided into:
- Subjectively invalid names - Names that have been rendered invalid by individual scientific judgement or opinion. Taxonomists may differ in their opinion and names considered invalid by one researcher, can be accepted as valid by another; thus they are still potentially valid names. It includes:
- Junior subjective synonyms - synonyms described from different types previously described as separate taxa.
- Junior secondary homonyms - species synonyms arising from merging two taxonomic groups previously considered separate. In this case, the taxa are separate species, but by chance, had the same specific name resulting in homonymy when their generic names are synonymized.
- Conditionally suppressed names - are special cases where a name which would otherwise have been valid has been petitioned for suppression by the International Commission on Zoological Nomenclatrue. This is usually because the junior synonym (the later name) has wider common usage than the senior synonym (the older name).
- Objectively invalid names - Names that have been rendered invalid for factual reasons. These names are universally accepted as invalid and not merely a matter of individual opinion as is the case with subjectively invalid names. It includes:
- Junior objective synonyms - names describing a taxon (the junior synonym) that have already been described by another name earlier (the senior synonym). ICZN follows the Principle of Priority, in which the oldest available name is applied in preference to newer names where possible.
- Junior homonyms in the family and genus group - names of families and genera which have the same spelling but refer to different taxa.
- Junior primary homonyms in a species group - species synonyms resulting from two different organisms being originally described with the same name spelled in the same way. Compare with the previously discussed junior secondary homonyms.
- Completely suppressed names - are special cases where a name is completely suppressed by the International Commission on Zoological Nomenclature. It is treated as if it had never been published and is never to be used, regardless of actual availability.
- Partially suppressed names - are special cases where a name is partially suppressed by the International Commission on Zoological Nomenclature. Unlike completely suppressed names, partially suppressed names are still acknowledged as having been published but is used only for the purpose of homonymy, not priority.
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