Chapter 6: Validity of Names and Nomenclatural Acts

Article 23. Principle of Priority.

23.1. Statement of the Principle of Priority. The valid name of a taxon is the oldest available name applied to it, unless that name has been invalidated or another name is given precedence by any provision of the Code or by any ruling of the Commission. For this reason priority applies to the validity of synonyms [Art. 23.3], to the relative precedence of homonyms [Arts. 53-60], the correctness or otherwise of spellings [Arts. 24, 32], and to the validity of nomenclatural acts (such as acts taken under the Principle of the First Reviser [Art. 24.2] and the fixation of name-bearing types [Arts. 68, 69, 74.1.3, 75.4]).

23.2. Purpose. In accordance with the objects of the Code (see Preamble), the Principle of Priority is to be used to promote stability and it is not intended to be used to upset a long-accepted name in its accustomed meaning by the introduction of a name that is its senior synonym or homonym (for certain such cases see Article 23.9), or through an action taken following the discovery of a prior and hitherto unrecognized nomenclatural act (such as a prior type fixation; for such cases see Articles 70.2 and 75.6).

23.3. Application to Synonymy. The Principle of Priority requires that a taxon formed by bringing together into a single taxon at one rank two or more previously established nominal taxa within the family group, genus group or species group takes as its valid name the name determined in accordance with the Principle of Priority [Art. 23.1] and its Purpose [Art. 23.2], with change of suffix if required in the case of a family-group name [Art. 34].

Example. The valid name of a genus formed by the union of the genera Aus 1850 and Cus 1870, and the subgenus Bus 1800 (transferred from the genus Xus 1758), is Bus 1800.

23.4. Application to Homonymy. The Principle of Priority requires that the relative precedence of homonyms, including secondary homonyms in the species group, is determined in accordance with the Principle of Priority (see Articles 23.1 and 23.2) and the Principle of Homonymy [Art. 52]; for its application to homonyms published simultaneously, see Article 24.

23.5. Application to spellings. The Principle of Priority applies to the spellings of an available name, unless an incorrect spelling has been preserved in accordance with Article 33.3.1, or, in the case of family-group names, with Articles 29.4 or 29.5. (For the preservation of unjustified emendations see Article

23.6. Application to nomenclatural acts. In accordance with the Principle of Priority the first nomenclatural act taken in respect of a name or a nominal taxon to achieve any of the following constitutes the only valid such act: i.e. acts taken under the First Reviser Principle [Art. 24.2], fixation of type species [Arts. 68, 69], first inclusion of nominal species in a genus-group taxon [Art. 67.2], designation of lectotypes [Art. 74.1.3] and neotypes [Art. 75.5] (types in the family group are fixed automatically and are not subject to subsequent fixation [Art. 63]; but for names published after 1999 see Article 16.2).

23.7. Application to collective groups and ichnotaxa. Except for the application of the Principle of Homonymy [Arts. 55, 56, 57],

23.8. Application to species-group names established on hybrids. A species-group name established for an animal later found to be a hybrid [Art. 17] must not be used as the valid name for either of the parental species, even if it is older than all other available names for them. Such a name may enter into homonymy. For names based on taxa which are of hybrid origin see Article 17.2.

23.9. Reversal of precedence. In accordance with the purpose of the Principle of Priority [Art. 23.2], its application is moderated as follows:

Recommendation 23A. If suppression desired. If in the opinion of an author suppression of the older name, rather than a change in the relative precedence of the two names involved, is desirable, in addition to taking action under Article 23.9.2 to maintain prevailing usage, the author should refer the case to the Commission with an appropriate recommendation for a ruling.

23.10. Erroneous reversal of precedence. If action taken under Article 23.9.2 is found later to have been taken in error in that conditions and were not met, the case is to be referred to the Commission. Prevailing usage must be maintained [Art. 82] until the Commission has made a ruling (i.e. an author discovering that such an erroneous action has occurred must not automatically use the older synonym or homonym).

23.11. Application of strict priority desired. If an author wishes to replace a name in prevailing usage by its older synonym when the conditions of Article 23.9.1 are met, he or she must apply to the Commission for a ruling under the plenary power [Art. 81].

23.12. Names rejected under former Article 23b. A name that was rejected between 6 November 1961 and 1 January 1973, by an author who explicitly applied Article 23b in force between those dates under the then current editions of the Code, on the grounds that it was a nomen oblitum (see Glossary) is not to be given precedence over a junior synonym in prevailing usage, unless the Commission rules that the older but rejected name is to take precedence.

Preamble | Articles 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 | Glossary Appendices Constitution


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