The two dots over the letter i are called “diaeresis” or “umlaut”. The diaeresis is a diacritical mark that consists of two dots placed over a letter, usually the letter i or u. The diaeresis indicates that the letter should be pronounced as a separate vowel sound rather than being combined with the preceding vowel.
The diaeresis is also sometimes called an umlaut, especially when it appears over the letter u in German. However, technically speaking, the umlaut is a different diacritical mark that changes the sound of a vowel, while the diaeresis simply indicates that two vowels should be pronounced separately.
The origin of the diaeresis can be traced back to ancient Greece, where it was used to indicate that two vowels should be pronounced separately. The Romans also used a similar mark, which they called the “dieresis”. In medieval Europe, the diaeresis was used in Latin and other languages to indicate that two vowels should be pronounced separately, especially when they appeared in diphthongs. Later on, the diaeresis was also used in German to indicate the umlaut sound.
In English, the diaeresis is not commonly used, but it is occasionally seen in words borrowed from other languages, especially French. For example, the word “naïve” includes a diaeresis over the letter i to indicate that it should be pronounced as a separate vowel sound. Similarly, the word “coöperate” may include a diaeresis to indicate that the two o’s should be pronounced separately.
In conclusion, the two dots over the letter i are called diaeresis or umlaut. The diaeresis is a diacritical mark that indicates that two vowels should be pronounced separately, while the umlaut is a diacritical mark that changes the sound of a vowel. The diaeresis has a long history in the development of written language, and while it is not commonly used in English, it can still be seen in borrowed words from other languages.