Due to the long history of the Greek language, it is hard to point out specific linguistic differences between distant periods, such as "ancient", and "modern", Greek. For example the pronunciation of Beta, Gamma and Delta is commonly regarded as an important phonetic difference between Ancient and Modern periods; however evidence[citation needed] suggests a fricative pronunciation of Gamma as early as the 4th century BC in Boeotian, Elean, Pamphylian, and possibly even vulgar Attic, and modern pronunciation may be derived from this[citation needed] (this point is debated among scholars). The only way to analyse the evolution of Greek until modern times, is to view the language as a whole.[citation needed] This is done by examining all its four periods, whose chronological boundaries are symbolic.

The development from Ancient Greek to Modern Greek has affected phonology, morphology, and vocabulary.

The main phonological changes occurred during the Hellenistic and Roman period (see Koine Greek Phonology for details), and included:

• replacement of the pitch accent with a stress accent
• simplification of the system of vowels and diphthongs (loss of vowel length distinction, monophthongization of most diphthongs, and some significant steps of iotacism)
• development of the voiceless aspirated stop consonants phi and theta to voiceless fricatives (the similar development of chi may have taken place later)
  
• possibly development of the voiced stop consonants — delta, beta and gamma — to voiced fricatives (the date is discussed among scholars)

The morphological changes affected both nouns and verbs. Some of the changes to the verbs are parallel to those that affected the Romance languages as they developed from Vulgar Latin — for instance the loss of certain historic tense forms and their replacement by new constructions — but the changes to the nouns have been less far-reaching. Greek has never experienced the wholesale loss of word-endings and noun cases that has for instance made Spanish, Portuguese, French and Italian separate languages from Latin.