1. Genetic Relationships

2. Genetic relationships
The processes of language change, it has been seen, invariably produce ever greater differences between the regional varieties of a language.
If such regional changes were to accumulate without limit for centuries, they would eventually become so different from one another that they would cease to be mutually comprehensible.
A time would come when we would be forced to speak, not of different dialects, but of different languages.
It is perfectly clear that such fragmentation of single languages into several different languages has happened countless times before.

3. Genetic relationships - Romance languages
About 2,500 years ago, Latin was an obscure little language spoken only in and around the small city of Rome.
But the Romans proved to be ambitious, skilled in diplomacy and powerful in war, and within a few centuries they had carved out an empire consisting of the entire area around the Mediterranean plus much of western Europe and the Balkans.
Throughout the Roman Empire Latin was the language of administration, and in time it came to displace some dozens of earlier languages, as the subjects of the Empire gave up their own languages in favour of the more prestigious Latin.
Hence Latin became the first language of several million people in Southern and Western Europe and in the Balkans.

4. Genetic relationships - Romance languages
Naturally, like any spoken language, Latin continued to change: The consonant /h/ was lost everywhere, The word-final /m/ was also lost, The vowel system of 5 long and 5 short vowels and 3 diphthongs was dramatically reorganized into a new system of 7 vowels without length distinctions and 1 diphthong, Velar plosives came to be palatalized before front vowels, The rich case-system began to collapse and to give way to the increasing use of prepositions, New verbal inflections replaced some of the old ones, The preferred SOV word order of earlier Latin was replaced by SVO word order, New words were introduced.

5. Genetic relationships - Romance languages
By the early centuries of the Common era the spoken language had evolved into what was known as Vulgar (popular) Latin.
Despite the efforts of prescriptive guides to the writing of proper classical Latin, such as the celebrated Appendix Probi, compiled in the 3rd-4th century, regional variation continued.
When the Empire finally collapsed in the 5th century, there was no longer any significant resistance to the splintering of Latin into innumerable regional varieties.
Within another couple of centuries, speakers of Latin in Spain, France, Italy and the Balkans could no longer understand one another.
Latin had therefore effectively broken up into several quite distinct languages.

6. Genetic relationships - Romance languages
But for a while there was no way of identifying a few well-defined languages with recognizable boundaries: there was just a vast dialect continuum.
Eventually, however, some regional varieties began to acquire a measure of prestige.
Around 12th century the speech of the Mediterranean coast of France, Provençal, became the vehicle of a brilliant literature.
Similar important literary developments based on the speech of the east coast of Spain, Catalan, and on that of Tuscany in Italy, Tuscan, led to the expansion of these varieties.
In most cases, however, it was not literature, but politics, that proved to be decisive.

7. Shrewd and ambitious politicians and military men made Paris (in France) and Castile (in Spain) politically pre-eminent and the centres of power so that the respective local varieties went on to become the standard French and Spanish.

8. Eventually, the first regional and then national standards came to be imposed upon the dialect continuum, and a few major languages emerged, each representing a distinctive development of the spoken Latin of centuries earlier.
We might, if we chose, give these modern descendants of Latin names like ‘Parisian Latin’ and ‘Madrid Latin’, but instead, we speak of French, Spanish, Italian and so on.

9. Genetic relationships - Romance languages
We say that the Romance languages are genetically related, and they all started out as regional dialects of a single ancestral language, and we speak of them as constituting a single language family - in this case, the Romance family.
Whenever linguists find a group of languages that are clearly genetically related, we know immediately that the languages have developed from a common ancestor, a proto-language, in the case of the Romance family, the Proto-Romance.
We actually have records of something that can be more or less identified with Proto-Romance: Latin, and Vulgar Latin.
Historical linguists have been successful at identifying a sizeable number of such language families.

10. Tree model and wave model
Language families, generally have an internal structure, with some languages being particularly closely related and perhaps forming subgroups within the family.
It is desirable to have some way of representing such internal structure: the most widely used device is the tree diagram, introduced by August Schleicher in the mid 19th century.
We look for shared innovations, changes that have appeared in some members of the family but not in others: languages that do not share a particular innovation are thought to have split off early from the languages that do share it.
When languages retain some interesting characteristics of the parent language, we talk about shared archaisms.

11. Tree model - Germanic family

12. Tree model and wave model
One of the drawbacks of the tree models is that with arbitrary and sudden splits, they cannot represent the linguistic reality.
In 1856 Johannes Schmidt therefore proposed a very different way of representing language families, the wave model.
The wave diagram shows an altogether more complex picture than the corresponding tree.
A wave diagram shows quite graphically the continuing contact between dialects and languages that have already begun to diverge.
It does not allow us to represent earlier and later stages of languages at the same time, something that the tree diagram does very easily.

13. Wave model - Germanic family