Editing Language family (section)

===Establishment===
{{main|Comparative method}}
In some cases, the shared derivation of a group of related languages from a common ancestor is directly [[attested language|attested]] in the historical record. For example, this is the case for the [[Romance languages|Romance language family]], wherein [[Spanish language|Spanish]], [[Italian language|Italian]], [[Portuguese language|Portuguese]], [[Romanian language|Romanian]], and [[French language|French]] are all descended from Latin, as well as for the [[North Germanic languages|North Germanic]] language family, including [[Danish language|Danish]], [[Swedish language|Swedish]], [[Norwegian language|Norwegian]] and [[Icelandic language|Icelandic]], which have shared descent from [[Proto-Norse language|Ancient Norse]]. Latin and ancient Norse are both attested in written records, as are many intermediate stages between those ancestral languages and their modern descendants.

In other cases, genetic relationships between languages are not directly attested. For instance, the Romance languages and the North Germanic languages are also related to each other, being subfamilies of the [[Indo-European language family]], since both Latin and Old Norse are believed to be descended from an even more ancient language, [[Proto-Indo-European]]; however, no direct evidence of Proto-Indo-European or its divergence into its descendant languages survives. In cases such as these, genetic relationships are established through use of the [[comparative method]] of linguistic analysis.

In order to test the hypothesis that two languages are related, the comparative method begins with the collection of pairs of words that are hypothesized to be [[cognate]]s: i.e., words in related languages that are derived from the same word in the shared ancestral language. Pairs of words that have similar pronunciations and meanings in the two languages are often good candidates for hypothetical cognates. The researcher must rule out the possibility that the two words are similar merely due to chance, or due to one having [[Loanword|borrowed]] the words from the other (or from a language related to the other). Chance resemblance is ruled out by the existence of large collections of pairs of words between the two languages showing similar patterns of phonetic similarity. Once coincidental similarity and [[Loanword|borrowing]] have been eliminated as possible explanations for similarities in sound and meaning of words, the remaining explanation is common origin: it is inferred that the similarities occurred due to descent from a common ancestor, and the words are actually cognates, implying the languages must be related.<ref>{{cite book|last=Campbell|first=Lyle|title=Historical Linguistics|date=2013|publisher=MIT Press}}</ref>

====Linguistic interference and borrowing====
When languages are in [[Language contact|contact with one another]], either of them may influence the other through [[Language transfer#Broader effects of language transfer|linguistic interference]] such as borrowing. For example, [[French language|French]] has influenced [[English language|English]], [[Arabic language|Arabic]] has influenced [[Persian language|Persian]], [[Sanskrit]] has influenced [[Tamil language|Tamil]], and [[Chinese language|Chinese]] has influenced [[Japanese language|Japanese]] in this way. However, such influence does not constitute (and is not a measure of) a genetic relationship between the languages concerned. Linguistic interference can occur between languages that are genetically closely related, between languages that are distantly related (like English and French, which are distantly related [[Indo-European language]]s) and between languages that have no genetic relationship.