There are much debate of when two dialects become languages. Apart from non-linguistic reasons like politics, quality of understanding is most often used to decide whether two dialects are effectively two languages.

However, is there anyone (academics preferably) stating something like a percentage of words being the same? And if so, what percentage are they proposing?

  • This could be useful for engines like Google, to distinguish quantitatively between languages and dialects. I realize however that this only would work for written language, which again could be "polluted" by non-linguistical things like politics.
    – Flying
    Dec 4, 2014 at 19:06
  • 1
    For each pair of candidates, find their linguistic distance and see if it exceeds a certain threshold. If a certain candidate is "far" enough from the others, that's a language. linguistics.stackexchange.com/questions/3006/… Dec 4, 2014 at 20:01
  • Making hard qualifying criteria can be tricky when you're dealing with dialect continuums. If you're not careful, you might end up saying that (for instance) Portuguese and Galician are dialects of each other, but then likewise Galician and Eonaviego, Eonaviego and Asturian, Asturian and Spanish, Spanish and Aragonese, etc. But if PT=GL, GL=EON, EON=AST, AST=ES, ES=ARG, ARG=CAT, CAT=SAR, SAR=COR, COR=FR (or any number of other paths one could take)... would we consider Portuguese and French to be just dialects? Logic would demand it, reality, less so. Dec 4, 2014 at 20:26
  • 4
    Lexical similarity is not enough. Mutual intelligibility requires grammatical similarity as well. Dec 4, 2014 at 21:26
  • The percentage of words is something that doesn't make much sense, because even the speakers of the same language use other words to describe the same thing, there are immense differences between 2 generations living under one roof. The academic definitions will vary from country to country and will be mostly politically or culturally driven.
    – user1609
    Dec 10, 2014 at 8:37

1 Answer 1


There are many measures of lexical similarity or linguistic distances but neither can tell you whether something is a dialect or a language outside a very constrained context. It is easy to come up with a measure for a particular purpose such as determining historical developments or automatically recognizing different languages in a corpus.

But what determines a language is as much a social and political matter as it is a question of linguistics. Even mutual intelligibility is not a solution because whether speakers of different languages can understand each other depends not just on pure lexical closeness but also on mutual exposure (which can often be assymetrical). Also, this mutual intelligibility may only be limited to a small subset of the language or only to certain subpopulations.

Compare these two sentences saying 'How do you like it here?' in Czech and Slovak:

  • Jak se ti tady líbí? (CZ)
  • Ako sa ti tu páči? (SK)

They only share one lexeme completely and one with some level of similarity (plus 'tu' is also used in Czech), yet, any Czech of my generation would not even blink twice over the Slovak version. Yet, a small Czech child thought it was English when meeting a Slovak linguist on a holiday abroad. Czech and Slovak are very close (so close that there were even attempts to call them Czechoslovak), yet young Czech speakers are exposed to Slovak less and less and find it difficult to understand Slovak without some considerable effort. Slovaks tend to have more exposure to Czech and therefore, tend to understand Czech better. Things become even more difficult when you look at Czech and Slovak dialects because some of them are closer to each other than to their respective standards.

This is just one small illustration of how difficult it is to make a categorical statement over whether something is a dialect or a language unless you also state what purpose the distinction is serving. But sometimes one purpose is more important than another. For instance, product labels are always bilingual in Czech and Slovak, yet, in all cases I can recall they have a lexical similarity between 90%-100% (at a guess much more than a typical utterance). Nevertheless, it is considered important to keep both languages separate for a variety of reasons that transcend questions of mutual intelligibility.

So you need to be explicit about why you want to know this and what you're planning to do with the information. But if the question is just a matter of general interest then no, there's no one percentage of similar words that will suffice to labels something a language or a dialect.

  • 2
    Thanks for the correction. Example of the asymmetric competence in the Czech-Slovak relationship. Dec 7, 2014 at 9:50
  • I think the perception (lg vs lect) has something to do with how much effort speakers and listeners have to go to in order to establish a comfortable interlanguage. Nobody ever gets native-like competence in a language learned later; there's always something new to bite you, if infrequently. But the kind of distinction between Czech and Slovak you refer to would no doubt pass without notice or comment in speech, a matter of a Czech accent, entirely understandable in context.
    – jlawler
    Dec 7, 2014 at 16:26

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.