Structure is more familiar to us in things we see than in things we hear. We build structures to inhabit; we observe structures in the natural world such as trees or coral reefs. Musical structure is often visible, too; we can see it in the physical movements that produce musical sounds, in the dance moves drawn from musical rhythms, and in the notation used to represent musical ideas. While any of these visible manifestations of musical structure could serve as a useful place to start our treatment of structured musical time, it is perhaps easiest to begin with the visible traces that are captured in standard music notation.