I know that languages change over time and they also diverge, which should decrease mutual intelligibility, but usually they do so in the way that keeps bunch of languages more or less together, while distancing them from their common ancestor.

It is easy to find facts like "bilingual dialog is generally possible in Scandinavian countries" and you can even get some precise numbers like "Italian has 89% similarity to French".

But its there a way to compare or test mutual intelligibility, to say, Italian and Latin (I know Italians generally can't read Latin, but they possibly also can't understand French)? Or can we say which language is closer to English, German or P. Germanic?

P.S. Actually, there was said "89% lexical similarity to French", I'm not sure what's the precise meaning.

2 Answers 2


This is perhaps not so much a straight answer as a suggestion in the right direction, but I hope it may prove useful.

First and foremost I would say that mutual intelligibility is not a property of languages, but a property of scripts and/or speech (which is why is seriously doubt that one can boldly say that Italian has 89% similarity to French, because who knows what properties that is based on). Languages that may be subject to very similar phonological processes, can be subject to very different morphological/syntactic processes. Languages therefore can be similar in either speech or script. I think there are not that many languages that are very similar when it comes to speech AND script. I would say this is not even very remarkable, because if a language is really similar in both speech and script one language would probably fade out.

Now, when it comes to mutual intelligibility (keeping in mind the difference in speech and literature), I think there may be several measures possible for each. For speech phonological processes (deletion, assimilation, usage of reduction, voicing and devoicing at certain points, stress, etc.) and pragmatics (how to respond in certain situations, methods of deixis, figurative use of language, etc.) can be of help. When it comes to script, syntactic processes (have a look at X-bar theory, usage of Parts Of Speech, distribution within and outside POS) and morphological processes (reduplication, affixation, modification of stems in certain environments, etc.) will probably give you heaps of information to discuss.

  • Raoul Buurke, agreed. Two languages can be very close 'on paper' but still be mutually unintelligible. Take the example of English and Danish: not too far apart in the IE tree, and also cross-fertilized later in the British Isles, but the average British tourist in Copenhagen would be totally lost were it not for the fact that most Danes speak excellent English. I also think that an Italian with no knowledge of French would find that language impossible on first exposure. Jan 29, 2016 at 11:09

When you want to test mutual intelligibility you need to do experiments with test persons. Note, that the mutual intelligibility is not a symmetric relation, in general there is a difference in the intelligibility of language A to native speakers of language B vs. the intelligibility of language B to native speakers of language A.

Tanja Augustinova has done a lot of research on mutual intelligibility of Slavonic languages, her publication list can be found here:


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