With the possible exceptions of constructed languages, languages seem to evolve. As a real-world example, we note that Latin has evolved into Italian, French, Spanish, Portuguese, Romanian, etc.

What defines the transition between an ancestor language and a descendent language? At what point do we say "These people in the Italian peninsula are no longer speaking Latin; they are speaking Italian"? Similarly for the other Romance languages, and for the split between Spanish and Portuguese.

Carrying that further, at what point does Puertoriqueño cease to be a dialect of Spanish, and take on its own identity as a language? Similarly for Brazilian vs Portuguese, or the other various dialects of Spanish in Latin America, or even English/England vs English/Australia vs English/North America?

(Note: I'm interested in, for lack of a better term, the linguistic constraints that define the difference, rather than the politico-geographical factors that influenced the development of those constraints. For the historical developments of $ModernRomanceLanguage from Latin, or Portuguese from Spanish, I'm also curious about the when.)

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    In philosophy, this is known as "the demarcation problem." It occurs when we feel the need to draw a line in the sand between two things when there is actually a continuum between them. We run into the same issues in science with the idea of species. As far as we can tell, nature has no concept of "species." Everything is on a continuum. But it proves so terribly valuable to be able to differentiate between a dog and a horse that we draw the lines anyways. – Cort Ammon Aug 7 at 19:05
  • See also the Ship of Theseus paradox – Timbo Aug 8 at 0:21
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    As soon as it can no longer reproduce with other ... wait, no that's a different thing – Azor Ahai Aug 8 at 1:23
  • In the case of Romanian, the demarcation point is its encounter with Slavic tongues, and the subsequent linguistic influence. – Lucian Aug 10 at 4:40
  • At what point do we say "These people in the Italian peninsula are no longer speaking Latin; they are speaking Italian"? - Such point doesn't exist; from Latin to Romance languages there are at least three rupture points (Latin/Vulgar Latin, Vulgar Latin/Romance, and Romance/Romance languages). – Luís Henrique Aug 11 at 0:31

This is a difficult question. Greek is perceived as one language despite the fact that Classical Greek is no longer intelligible for a native speaker of Modern Greek without exposure to the classical language. For the Romance language, the split into several different descendants (Italian, Provençal, French, Spanish ...) surely helped to form different identities and not seeing Italian as kind of "popular Latin".

Chinese is seen as one language mainly for political reasons, although different "dialects" of Chinese are not mutually intelligible as spoken languages. On the other side, Croatian, Bosnian, Serbian, and Montenegrin are considered different languages for political reasons, and there are ongoing language-planning activities to tear the languages further apart.

All in all, the perception of one language or two language is not governed by linguistic criteria, but by political and cultural criteria.

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    So the answer is, "after the Romans start calling their language 'Italian'?". – user6726 Aug 7 at 16:51
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    In principle, yes. – jknappen Aug 7 at 17:04
  • An even more difficult case is Macedonian, which some claim is a empty name used for a variety of Bulgarian. This is very much a political dispute. – Colin Fine Aug 9 at 20:40
  • "All in all, the perception of one language or two language is not governed by linguistic criteria, but by political and cultural criteria." - To a certain extent. I am sure that Brazilians could easily declare that they speak Brazilian and not Portuguese, and that would probably foster the notion that it is a different language from that of Camões. But no amount of Brazilians stating that their language is merely new-world Latin will make Brazilian Portuguese a variant of Latin. The linguistic differences are too stark for that to be taken in serious. – Luís Henrique Aug 12 at 12:45
  • "after the Romans start calling their language 'Italian'?" - To notice, "Romans" (as in, "people from Rome") never started calling their language "Italian". The language they call "Italian" is Tuscan, not the language they spoke before unification. You may call this a Dantesque situation, which is literally true, but Modern Italian is not in direct continuation of what used to be spoken in Rome... – Luís Henrique Aug 12 at 12:50

The philosophical answer that it is a continuüm is correct, but natural borders like seas, rivers, mountain ranges and even city limits have their influence on languages. It is not only political and cultural, but also natural that changes in languages and mingling with other languages or not create enough differences that you can at a certain point get away with calling it a different language. In the most extreme case it could be said about two groups speaking an identical language with one of them having a word the other group does not use. That said a language is different when it has its own word base that differs from the language it mostly came forth from. Put the line wherever you wish, as long as it is founded. Even within city limits...

At what point a language changes so much that it becomes another language?

That is a difficult question, that probably can only be answered in hindsight. At no moment in the convoluted history of Romance languages, anyone woke up and realized, "gee, this thing I am speaking is not Latin, it is, wow, French". People just spoke the language of their time and place, or one or more of the languages of their time and place (in France, likely, Vulgar Latin and Frankish).

At that time in history, people certainly distinguished Latin - the language in which the priest said the mass, which was mostly incomprehensible to them - from the language they actually spoke, which was, for lack of a better word, generally called "Vulgar" or "Vernacular", and quite certainly didn't constitute a unified language - it was different in Lisbon or Catania, Nice or Santander. When in contact with people of different places, people would recognise that those from other places spoke a different language - sometimes so far apart as to be unintelligible, sometimes close enough to be described like, "those damn Genoese and their ridiculous and wrong way of speaking". But contact with foreigners was rare, and probably most accessible to people who could manage some Latin - Medieval Latin, already quite different from Classic Latin, but that remained the language of high culture throughout Europe during the Middle Ages.

When the Romans conquered Western Europe, there were already several differences between the language spoken by the Roman elite and the Roman populace, to which most of the conquering soldiers belonged. It is this variant of Latin - Vulgar Latin - that originated the several Romance languages (with the exception, I think, of Sardinian, which is more related to Classic Latin). To the extent that Romans were conscious of this dichotomy between their standard language and the language effectively spoken by common people, the divide is very old. Ciceron probably knew his language was different from the language of his servants, though he probably framed this as "proper Latin" versus "wrong", or "debased", Latin.

Vulgar Latin then evolved differently at the different parts of the Roman Empire/influence area. At some point in history, the differences were big enough that we can no longer speak of "Vulgar Latin" as one language. Unfortunately, this was mostly an undocumented process: people actually changing the language were illiterate, so they didn't write their language; and literate people wrote in Medieval Latin, not in Vulgar, and weren't really interested in writing about the commoners' language(s). But at some point the language spoken in the Iberic Peninsula was Iberic Romance rather than Vulgar Latin.

Apart from the scant documentation, we can use comparative method to understand such changes.

For instance, here we have the history of a single word, from Classic Latin to Modern Portuguese:

Classic Latin: genu- (/genu/)

Classic Latin (diminutive of the former): genuculu- (/genukulu/)

Vulgar Latin: genuclu (/ʒenuklu/)

Iberic Romance: *genollo (/ʒenoʎo/)

Old Portuguese: jeolho (/ʒeoʎo/)

Modern Portuguese: joelho (/ʒoeʎu/ or /ʒweʎu/))

How do we know that the order of the changes is that, first /g/ to /ʒ/, then /kl/ to /ʎ/?

Apart from documentation (we have Old Portuguese texts with the word "jeolho", for instance), we know that Medieval Latin has /ʒ/, and not /g/, so this sound must have changed very early and was probably done in Vulgar Latin; we know that all Romance languages have changed /kl/ into something different, so that it must have happened later, when Vulgar Latin was morphing into several different Romances; we know that Portuguese alone dropped intervocallic "n" (compare Portuguese "geral" to Spanish "general", so that must have been even later, when Iberic Romance was dividing into Galician-Portuguese and Castillian.

This process then intertwined with the political process of the formation and unification of modern nation-States. At this point, the local elites of Portugal, Spain, France, decided that they would be better served by making their local languages literate than by trying to repopularise Latin, as it would help in constructing the borders, and in creating a national ideology that could justify the existence of the nation-State. At that point we have the earliest literature in those languages. This process was unfortunate for several Romance languages that didn't correspond to the political boundaries - Mirandese, Occitan, Catalan, Leonese, etc. And it originates the saying, "a language is a dialect with an army", from which it is often deduced that the differences between languages is more political than linguistic (but notice, the army, and the State in general, are, besides obviously political entities, also glossopoietic) entities: military terms are coined by the army (and navy), and courts, police, universities, public schools, also coin a huge vocabulary).

In the specific case of Italy, the political process of unification of the nation-State happened much later, only in the 19th century, which favoured the permanence of several different local languages - Venetian, Sardinian, Sicilian, Tuscan, Neapolitan, Emilian, Lombard, Piedmontese, Calabrian, etc. - not all of which even belong to the same Romance branch (Sardinian is Insular Romance, Venetian is Western Romance, while most of the others are Southern Romance). So things in Italy are even more complicated than in Portugal, France, or Spain: while those have had national languages from the end of the Middle Ages, Italy chose Tuscan its national language, or based its national language on Tuscan (mainly due to the literary and cultural importance of Dante), only in the 19th century, much after everyone in the peninsula was very sure that what they spoke was not Latin.

So, at what point we say "These people in the Italian peninsula are no longer speaking Latin; they are speaking Italian"? At no point. They stopped speaking Classic Latin at the end of the Antiquity, when cultured Latin evolved into Late Latin (which in turn evolved into Medieval Latin later), while popular Latin evolved into Vulgar Latin. At the Middel Ages, they were speaking several different languages, which can be linguistically grouped into three different "families", Western Romance in the North, Insular Romance in Sardinia, and Southern Romance in most of the Peninsula and in Sicily. "Italian" as we know it was one of these Southern Romance languages, namely Tuscan, and spoken by a very small minority of the population up to the 1860, when Italy became a unified nation-State, and its State deliberately choose it a the national language, and enforced via public education (and active repression of the local languages, which became collectively know as "dialects").

As for "the split between Spanish and Portuguese" (which is really the split between Castillian and Galician-Portuguese), it happened in the High Middle Ages, certainly before the split the Condado Portucalense and the Kingdom of Spain. But then the political split reinforced the linguistic divide, making the languages further evolve apart from each other (and sparing Portuguese the fate of the minoritary languages of Spain).

And "at what point does Puertoriqueño cease to be a dialect of Spanish, and take on its own identity as a language? Similarly for Brazilian vs Portuguese, or the other various dialects of Spanish in Latin America, or even English/England vs English/Australia vs English/North America?"

At what point in time it is impossible to know. Modern communication doesn't favour the division of languages - and, so, the process is bound to be slower, possibly much slower, than the split of Latin into several languages. Unless, of course, there is a collapse of modern civilisation, that breaks the communication system apart, so that people in Puerto Rico, Brazil, or Australia, are no longer in touch with Spain, Portugal, or England (which, as a second thought, is what happened to the Roman Empire too, so the odds are, if there is a civilisation collapse, in half a millenium, when finally Venezolans rediscover Spain, people in Latin America will be unable to understand Spaniards, and conversely). At what point in linguistic terms, when the spoken varieties of those languages become mutually incomprehensible (text is more conservative, and may allow for the fiction of linguistic unity, perhaps useful for political purposes).

  • This is a very interesting answer; would it be safe to say that an "accurate oversimplification" from a linguistic, ignoring political, point of view would be that you have separate languages instead of dialects when mutual intelligibility either ceases to exist, or is so low that each speech must be specifically studied to achieve intelligibility? – Jeff Zeitlin Aug 12 at 17:36
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    I thought the development of palatalized *g in Vulgar Latin was something like gʲ > j > dʒ > ʒ, with the step dʒ > ʒ occurring relatively late: standard Italian still has [dʒ], and old loanwords from French into English indicate that Old French had [dʒ] – sumelic Aug 12 at 20:14
  • Gets tricky when, say, given a historical language X for cultural/political reasons they get termed, say, Y and Z, despite being incredibly similar (and remain often virtually identical, accent and orthography notwithstanding). But then Y breaks into Y1 and Y2, and while Y1 stays virtually identical to Z, Y2 becomes markedly different. Despite Y1 and Y2 being so different, for political/cultural reasons, they still are considered the same. I'm of course speaking here of pt-PT/BR and gl-ES. – guifa Aug 12 at 21:02

One keyword here is holotype. E.g. Carl von Linne used his brother as type specimen for the Homo Sapiens, and the first Archaeopterix finds were all named differently because the relation among them wasn't clear. Definitions for familiar relations are based on a set of similarities. You could even have a phylogenetic tree of clade systems.

Classical Latin had Cicero, Ancient Greek had Homer, Standard High German has the guy in the evening news, the Queen's English is well received and so on. So far this is easy, but language depends on communication and dialogue, not a single person. Hence groups of speakers are compared. The biggest, accepted grouping is the language family, for example Indo-European or Afro-Asiatic. Some go even further and assume all extent languages developed from a common source. Hence I assume proscription to some extend means what was said for the first time, description is copying, and prescription is what was said before. So a language changes by faulty description and other proscription.

The real question is, what is a language. My take is, language is uncountable, dialect is individual, and the plural, languages, is a multitude of instances of using the language. Which is a fuzzy set (see wikipedia; I never learned more about it).

At the small scale, even a single individual will make use of code switching for example, make up new sentences everyday and learn new words. The pressing question is how even a single word is learned, defined and produced, reinterpreted, and reproduced. Impressions left by a forbearer are as important, in the simple case, as much as imagination is in the big picture, from baby speech to high poetry. Hence I don't completely subscribe to the single-mother hypothesis.

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