Smail, Daniel Lord (2008): On Deep History and the Brain. An Ahmanson foundation book in the humanities. Berkeley: University of California Press, ISBN: 9780520258129 (utdrag på Jstore
leidenuniv.nl
openaccess.leidenuniv.nl
Jagersma, Abraham Hendrik (2010): A descriptive grammar of Sumerian (PDF) (Thesis). Leiden: Faculty of the Humanities, Leiden University. s. 15. Sitat: «In its fully developed form, the Sumerian script is based on a mixture of logographic and phonographic writing. There are basically two types of signs: word signs, or logograms, and sound signs, or phonograms.»