A smooth, uniform surface. A sharp, hard object runs over it, leaving a trace of its passage. Someone intentionally performing this action in the hope that someone else will see the trace. Underlying the intention, an assumption, not spelled out and yet necessary. The first agent is assuming that the second agent will see, in that trace, the same meaning that he or she sees. If the first agent sees the shape of an animal, so will the second. If he or she sees that the trace partitions the space of the drawing with rhythm and balance, the second agent will also see that rhythm and that balance. In a nutshell, this is the communicative mechanism that underlies the creation and the use of drawings. It’s all in that simple assumption. Yet such a minimalistic procedure has produced, and continues to produce, a huge quantity of work, continuously innovating solutions under the spur of novel communicative needs.