The basic scientific name of a bird species consists of four parts; Fringilla coelebs Linnaeus, 1758, is the full scientific name of the Common Chaffinch. The first two parts, the binomen Fringilla coelebs, are written in a Latin or neo-Latin form and traditionally printed in italics.
The first part of the name denotes the genus, distinguishing a group of related species or an isolated, distinctive species. It must be in the form of a noun or a substantivised adjective treated as a noun, it must be unique in the zoological world, and it must begin with an upper-case letter. If the same genus is referred to in subsequent but different specific combinations the convention is to use the initial abbreviation for the generic term, provided it does not cause confusion (Turdus migratorius, T. philomelos, T. viscivorus (which are all in Turdus); but not Tchagra australis, T. jamesi, T. tchagra, T. senegalus, T. zeylonus, where T. zeylonus refers to Telophorus zeylonus).
The second part of the binomen, beginning with a lower-case letter, is the specific or trivial name, distinguishing the species within the genus, and, although chimaerical, is commonly an adjective or a noun in the genitive case. Only in combination with a generic name does it have any validity or make any sense, but it can be used in more than one genus; thus Cissa hypoleuca Salvadori & Giglioli, 1885, Ficedula hypoleuca (Pallas, 1764), Grallaria hypoleuca P. Sclater, 1855, Poecilodryas hypoleuca (G. Gray, 1859), Pterodroma hypoleuca (Salvin, 1888), and Turdoides hypoleuca (Cabanis, 1878) are all valid names in zoology. Within the genus, however, no two species, subspecies or forms (taxa) may bear the same specific name. In 1823 the German ornithologist Martin Lichtenstein described a new black-headed wagtail as Motacilla melanocephala. That name was preoccupied by Motacilla melanocephala J. Gmelin, 1789, the noisy Sardinian Warbler of the Mediterranean, and Lichtenstein's later name was no longer valid by reason of homonymy. In the absence of a junior synonym Lichtenstein's wagtail was later described as Motacilla feldegg Michahelles, 1830. If the same genus and species names are referred to in subsequent but different subspecific combinations the convention is to use the initial abbreviation for both the generic and specific terms (Sayornis nigricans semiater, S. n. aquaticus, S. n. amnicola, the two latter names being abbreviations for Sayornis nigricans aquaticus and Sayornis nigricans amnicola).
The third and fourth parts of the Common Chaffinch's scientific name, Linnaeus, 1758, reveal the author of the specific name and the year in which that name was first validly published as a binomen. The author’s name placed in parentheses after a specific name indicates that the current generic classification differs from that assigned by the original author. For example, the Lesser Whitethroat Sylvia curruca (Linnaeus, 1758) was originally described by him in the genus Motacilla.
Systematic publications, such as check-lists, hand-books and synopses, generally give a full citation of both generic and specific names, including original publication details, identification of the type species of the genus, type locality of species, and comprehensive list of synonyms. Non-systematic scientific works, popular books, field-guides and magazines usually give only the binomen.
Many species are divided by systematists into subspecies or races, which are populations of the species occupying a distinct geographic range and distinguished by recognizable morphological characters from other populations of the species. Species subdivided into subspecies are polytypic, those for which no subspecies are recognized are monotypic. Because of the continuity of the evolutionary process, some subspecies are so diverse that they are considered by ornithologists to have crossed the specific threshold and become species in their own right. In nomenclature, subspecies are designated by adding a third name to the binomen, creating a trinomen. The subspecies of the Common Chaffinch breeding in Europe and western Siberia is known as Fringilla coelebs coelebs, the nominate subspecies, whose trinomen, created by repeating the specific epithet, reflects an accident of geography or history rather than precedence or relationship. It can be morphologically distinguished from populations breeding in the British Isles Fringilla coelebs gengleri, the Crimea Fringilla coelebs solomkoi, and others found elsewhere in the species’ Palaearctic range. At least two of these forms, Fringilla coelebs spodiogenys of North Africa, and Fringilla coelebs canariensis of the Canary Islands, Madeira and the Azores are considered by some as distinct species, Fringilla spodiogenys and Fringilla canariensis. Extreme cases of polytypism include the Island Thrush Turdus poliocephalus of South-east Asia and the south-west Pacific with over fifty named subspecies, and the Song Sparrow Melospiza melodia of the Nearctic with about forty subspecies.
Neither generic nor specific names need to be descriptive, accurate or relevant, and they cannot be rejected or corrected merely for being erroneous in these respects, although some earlier authors sought to do so. Many names coined in the early years of systematic zoology are now known to be inappropriate, having been based on inaccurate plates or drawings, specimens affected by poor storage conditions, lay descriptions, mistaken provenance, mixed-up specimens, fraud, or human frailty and error.