Languages evolve and diversify over time, and the history of their evolution can be reconstructed by comparing modern languages to determine which traits their ancestral languages must have had in order for the later developmental stages to occur....

Italy has always had a distinctive dialect for each city because the cities, until recently, were thought of as city-states. Those dialects now have considerable variety....

Japanese dialects typically differ in terms of pitch accent, inflectional morphology, vocabulary, and particle usage. Some even differ in vowel and consonant inventories, although this is less common....