Practically, when a naturalist can unite by means of intermediate links any two forms, he treats the one as a variety of the other, ranking the most common, but sometimes the one first described as the species, and the other as the variety.
Praktikan naturalistak, zeinahi bi forma bitarteko lokarriz batu ahal dituenean, bata bestearen aldakitzat hartzen ditu, arruntena, baina batzuetan lehenbizi deskribaturikoa, espezietzat eta bestea aldakitzat sailkatuz.