For millennia humans have used visible marks to communicate information. Modern examples of conventional graphical symbols include traffic signs, mathematical notation, and written language such as the text you are currently reading.
This book presents the first systematic study of graphical symbol systems, including a taxonomy of non-linguistic systems—systems such as mathematical and musical notation that are not tied to spoken language. An important point is that non-linguistic symbol systems may have complex syntax, if the information encoded by the system itself has a complex structure.
Writing systems are a special instance of graphical symbol system where the symbols represent linguistic, and in particular phonological information. I review the properties of writing and how it relates to non-linguistic symbols. I also review how writing is processed in the brain, and compare that to the neural processing of non-linguistic symbols. Writing first appeared in Mesopotamia about 5,000 years ago and is believed to have evolved from a previous non-linguistic accounting system. The exact mechanism is unknown, but crucial was the discovery that symbols can represent the sounds of words, not just the meanings. I present the novel hypothesis that writing evolved in an institutional context in which accounts were dictated, thus driving an association between symbol and sound. I provide a computational simulation to support this hypothesis.
Human language has syntactic structure, and writing inherits the structure that language has. This leads to a common fallacy when it comes to undeciphered ancient symbols, namely that the presence of structure in a system favors the conclusion that the system was writing. I review recent instances of this fallacy, pointing out that known non-linguistic systems also have structure, so that the presence of structure is not very informative.
The book ends with some thoughts about the future of graphical symbol systems.