<Li> Widespread use . The binomial system of nomenclature is governed by international codes and is used by biologists worldwide . A few binomials have also entered common speech, such as Homo sapiens, E. coli, Boa constrictor, and Tyrannosaurus rex . </Li> <Li> Uniqueness . Provided that taxonomists agree as to the limits of a species, it can have only one name that is correct under the appropriate nomenclature code, generally the earliest published if two or more names are accidentally assigned to a species . However, establishing that two names actually refer to the same species and then determining which has priority can be difficult, particularly if the species was named by biologists from different countries . Therefore, a species may have more than one regularly used name; all but one of these names are "synonyms". </Li> <Li> Stability . Although stability is far from absolute, the procedures associated with establishing binomial names, such as the principle of priority, tend to favor stability . For example, when species are transferred between genera (as not uncommonly happens as a result of new knowledge), if possible the second part of the binomial is kept the same . Thus there is disagreement among botanists as to whether the genera Chionodoxa and Scilla are sufficiently different for them to be kept separate . Those who keep them separate give the plant commonly grown in gardens in Europe the name Chionodoxa siehei; those who do not give it the name Scilla siehei . The siehei element is constant . Similarly if what were previously thought to be two distinct species are demoted to a lower rank, such as subspecies, where possible the second part of the binomial name is retained as the third part of the new name . Thus the Tenerife robin may be treated as a different species from the European robin, in which case its name is Erithacus superbus, or as only a subspecies, in which case its name is Erithacus rubecula superbus . The superbus element of the name is constant . </Li> <P> Binomial nomenclature for species has the effect that when a species is moved from one genus to another, sometimes the specific name or epithet must be changed as well . This may happen because the specific name is already used in the new genus, or to agree in gender with the new genus . Some biologists have argued for the combination of the genus name and specific epithet into a single unambiguous name, or for the use of uninomials (as used in nomenclature of ranks above species). </P>

How many species can have the same scientific name
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