Gelb began a new phase in the study of writing systems by introducing “Grammatology”, a scientific approach to the study of writing which borrows methodology from linguistics (for a good history of the study of writing systems, see Daniels, “The Study of Writing Systems” in The World’s Writing Systems, ed Peter T Daniels and William Bright. (Oxford, 1996), 3-18).
Gelb presents a basic view of the evolution of writing from narrative art to symbol to pictographic system. Next, the leap of phonetization allows the correspondence of symbols with either words or sounds. From this developed syllabic systems and finally the alphabet.
Gelb has been criticized for over-systematizing in his principles of uniform development and economy (see Daniels, “Fundamentals of Grammatology”). The principle of uniform development states that writing always develops from logographic to syllabic to alphabetic, thus Gelb argued that the early West-Semitic scripts were not alphabetic but syllabic since the later Ethiopian syllabic script could not have developed from a true alphabetic script. Just as certain cuneiform signs can indicate a consonant plus the full range of vowels (e.g., wi, we, wa, wu), he maintained that the West-Semitic letters actually indicated a consonant plus an unmarked vowel. The matres lectionis then function as phonetic complements to mark the proper vowel. Only when the Greek system developed individual vowel letters was a true alphabet created.