true writing system must be able to represent graphically any utterance
of which a language is capable; incomplete systems, such as pictograms,
are called protowriting. The terms protowriting and writing
would seem to imply an evolutionary sequence, but we must be cautious. First,
writing has in no sense replaced protowriting. Instead, they exist side
by side. When we drive to an airport, the road signs constitute a protowriting
system of pictograms, and if the airport is in a country whose language
we do not speak, we navigate through the airport by means of another protowriting
Even if writing developed monogenetically in Sumeria, how it arose is not clear. One currently common theory argues that the culture began to use tokens of various shapes to keep economic tallies, then began to impress the tokens into clay tablets, then began to "draw" the tokens. From these graphical tallies, a pictographic protowriting system developed, which led in turn to true writing. The latter part of the model is a certainty; Sumerian pictographic protowriting developed into writing. The origin of pictographs in a token system, however, remains hotly debated.
How, and how often,
writing systems developed is not certain, but one certainty remains. The
world's oldest known true writing system, cuneiform, developed in Sumeria.