Language families can be divided into smaller phylogenetic units, conventionally referred to as branches of the family, because the history of a language family is often represented as a tree diagram. However, the term family is not restricted to any one level of this "tree"; the Germanic family, for example, is a branch of the Indo-European family. Some taxonomists do restrict the term family to a certain level, but there is little consensus in how to do this. Those who do affix such labels also subdivide branches into groups, and groups into complexes. They also aggregate families into phyla (also known as stocks, or superfamilies). Phyla are often used to aggregate American Indian language families. One method for doing all of this is called glottochronology.
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