There is a state of Greece in Europe. It appeared on the political map in the first half of the 19th century after breaking away from the Ottoman Empire. Greece was created with the military assistance of Great Britain and France with the connivance of the Russian Emperor Nicholas I.
The separatist-minded Greek intelligentsia, based, as it happens in such cases, abroad, has long dreamed of their own independent country. The basis of the new state, according to their plan, was to be the Orthodox faith and the Greek language. If everything seemed to be in order with faith, then the language had yet to be invented.
Believe it or not, at the turn of the 18-19th centuries, the Greeks did not have their own single national language in which to write the Constitution and other laws, to conduct office work. The Turkish language, which all Greeks understood, did not seem solid to use for these purposes.
Many common Greeks never knew Greek at all. They considered Urum (and some other similar Turkic languages) to be their native language. But the Constitution cannot be written in Urum. It was generally unwritten.
Other Greek commoners knew how to speak Greek. But not in the Greek it should be. They spoke in dialects derived from the medieval Byzantine (Romeian) language - for example, Pontic, Cappodocian and others. All these "Romeiki" remained archaic. Originally intended for oral communication, dialects had an extremely small vocabulary - no more than 4-5 thousand words. It was not possible to formulate not only the Constitution, a couple of its articles in such languages.
However, the ideologues of Greek separatism had a trump card - the so-called "ancient Greek" language. I do not know how ancient this language is, but it was not dead to that one. On the contrary, it actively and successfully developed in a certain environment.
As you can see, the "ancient Greek" language and the language of the Greek Phanariots are one and the same. In general, the situation resembles the situation in the Soviet Union. The central government allowed the representatives of the national borderlands to be educated. The national elites invented "ancient" history, "ancient" literature, declared that they were greatly oppressed and decided to secede.
"Ancient Greek" is undoubtedly great and powerful:
For writing the Constitution was quite suitable. But the trouble, written in ancient Greek wise laws, none of the Greek plebs will understand.
The cunning Greek intelligentsia found a way out of this situation. At first, Adamantios Korais, who lived in Paris, proposed the "middle way", combining the "spoken" and "ancient Greek" languages. This is how the first version of the modern Greek "caafverus" or "pure" language was born, which preserved the grammar and vocabulary of ancient Greek with the national pronunciation.
Soon, the "caafverse" was offered an alternative - "dimotics" - the second version of the modern Greek, allegedly systematized and purified "folk" language.
For a long time, "caafverus" and "dimotics" coexisted peacefully and not very much (it came to street clashes between supporters of one version or another). The state language was considered "caafverus". It was used for office work. It was studied in schools.
Naturally, there was an interpenetration between languages. More precisely, the words from the rich zakorom "caafverusy" flowed into the initially meager reserves of "dimotics". As a result, the latter developed to such an extent that in 1976 it was declared the official language of Greece. And the "caafverus", having done his job, is gradually being forgotten.