Adding a new dimension to the Pictionary task, Carrie Anne Thiesen et al (REF 2010) defined sets of referents within the same semantic domain, including such spheres as 'agriculture' and 'education' (Figure 3). One compelling outcome of this experiment was the innovation of compositional signs with one graphic element employed to constrain the inference to a given domain. Although the authors do not themselves draw this comparison, this innovation is remarkably similar to the function of so-called semantic determinatives that are witnessed in the four known independent inventions of writing in Sumer, Egypt, China and Mesoamerica (Figure 4).