Liz C has suggested this topic and, though we have done it in the past, it was a great success and led to some interesting discussions. Do you use any rules when formulating a new composition? What are those rules? Do they change over time? Are classical composition rules still relevant? Think of a painting which particularly appeals? What composition rules (if any) does it follow? Etc. etc.... Also, besides linear composition, there is colour composition and narrative composition. One school of thought is that composition is the art of directing the viewer through a painting/photograph. If so, why would this matter?