How do we know if two languages are related?


In these monthly discussions we answer one question about language in PNG and beyond. This month we are looking at the relationships between languages and how to judge whether two languages are related or not.
People sometimes ask me how they can tell if their language is “related” to another language. This is something we can measure and test using long established linguistic principles. But what exactly do we mean by languages being related?
It helps to think of languages and their relationships as being similar to human beings and their relationships. Think about your relationship with your brothers and sisters, cousins, and neighbours. You are very closely related to your brothers and sisters because you share the same parents and therefore almost all the same DNA. You also share a lot of shared history because you grew up with the same household rules, food, and behaviour. Your relationship with your cousins is also close, even though it is less strong than your relationship with your siblings. You share DNA (although less than with your siblings), family history (although at the grandparent, and not parent, level), and many of the same family rules and behaviour. Your relation with your neighbours is different. You probably don’t share any close DNA or family history with them, but your family and they may have traded tools or dinner recipes and spent so much time together that you think of them as relatives even if they are not.
Languages have the same relationships. Languages are in constant change. When people are in close proximity and feel they are members of the same group, their speech tends to change all in the same direction, and they remain one language community. But when groups of people split up and live in isolation from one another, their speech changes in different ways, eventually becoming different languages.
Some languages have a common ancestor from the near past, so we call them sister languages. The Kuanua language of the Gazelle Peninsula of East New Britain and the Ramoaaina language of the Duke of York Islands, for example, separated from each other only a relatively short time ago, so these sister languages share many similarities. They are both related to the languages of southern New Ireland, where the ancestors of their current speakers came from, but while this relationship is noticeable, it is less close than the one between Kuanua and Ramoaaina. Kuanua and Ramoaaina are like sisters, while the southern New Ireland languages are like their cousins.
Tolais and Bainings have lived next to each other ever since the ancestors of the Tolais migrated to New Britain, so it is not surprising that they have shared words back and forth. But this relationship is weak and not a genetic one. They are neighbouring, but unrelated, languages.
Linguists look at vocabulary more than grammar to establish how languages are genetically related, because grammar changes much more easily than vocabulary. The Austronesian languages, for example, historically have a subject-verb-direct object word order. But when the ancestors of the Motu people migrated to their present home and came in contact with languages there where the word order has the verb at the end of the sentence, they gradually changed their grammar to subject-direct object-verb. This is just like a Highlander learning how to make aigir from her Tolai neighbour. She might learn Tolai cooking techniques, but she remains a Highlander and not suddenly a member of her Tolai neighbour’s family.
Some types of vocabulary change more easily than others and are more resistant to borrowing. The more intimate the item–family, body parts, or basic words for the environment–the less likely the word is to change or be borrowed completely from another language. For example, if your language has a word for “father” similar to “tama”, a word similar for “breast” similar to “susu”, or a word for “five” and/or “hand” similar to “lima”, your language is probably a member of the widespread Austronesian language family. These common words have remained little changed over thousands of years, even though speakers of Austronesian languages have migrated to cover half the southern hemisphere.
Linguists compare 100 to 200 common words using lists such as the one developed by the American linguist Morris Swadesh in the 1950s to look for similarities and patterns between languages. Sometimes the similarities are there, but not immediately obvious. For example, when the ancestor of the languages of northeastern Europe became isolated from their neighbours, they gradually changed a “p” sound at the beginning of a word to an “f” sound. Thus we have English speakers in northern Europe saying “father” and “fish”, but Latin speakers in southern Europe saying “pater” and “piscis”. Linguists look for these kinds of regular sound shift patterns to see how closely or distant related languages are.
Of course, just as some unfortunate people are orphans without any living relatives, some languages have no known living languages with which they share a common ancestor. These are called language isolates. This may be because for one reason or another, any related languages have died out, or it may be because these languages have been separate for so long that it is no longer possible to find connections with other languages.
A good place to see the current stage of linguistic research into the relationship your language has with other languages is to look up your language at or Wikipedia (which usually has results usually gleaned from the website). There you will find diagrams and explanations listing the languages that are known to be closely related to yours as well as the larger language family to which your language belongs.
You and your friends can also conduct your own linguistic research by comparing words from languages you speak using a version of the Swadesh list that you can find at Are you and your friends linguistic siblings, linguistic cousins, or just neighbours?

  • Professor Volker is a linguist living in New Ireland, and an Adjunct Professor in The Cairns Institute, James Cook University in Australia. He welcomes your language questions for this monthly discussion at Or continue the discussion on the Facebook Language Toktok page.

One thought on “How do we know if two languages are related?

  • What are the steps in carrying out a research
    For two or more languages to know if they are related or not

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