The Sumerian language is generally regarded as a language isolate in linguistics because it belongs to no known language family; Akkadian, by contrast, belongs to the Semitic branch of the Afroasiatic languages. There have been many failed attempts to connect Sumerian to other language groups. It is an agglutinative language; in other words, morphemes (<answer>"units of meaning"</answer>) are added together to create words, unlike analytic languages where morphemes are purely added together to create sentences. Some authors have proposed that there may be evidence of a sub-stratum or add-stratum language for geographic features and various crafts and agricultural activities, called variously Proto-Euphratean or Proto Tigrean, but this is disputed by others.
What are morphemes?
"units of meaning"