Currently at the Media design seminar here at the Geneva School of Art and Design, we discussed this interesting way to explain the notion of modularity. Called, "the parable of the two watchmakers", It's from Herbert Simon and it nicely explains the relationship of simple and complex systems (organic and social):

"There once were two watchmakers, named Hora and Tempus, who made very fine watches. The phones in their workshops rang frequently and new customers were constantly calling them. However, Hora prospered while Tempus became poorer and poorer. In the end, Tempus lost his shop. What was the reason behind this? The watches consisted of about 1000 parts each. The watches that Tempus made were designed such that, when he had to put down a partly assembled watch, it immediately fell into pieces and had to be reassembled from the basic elements. Hora had designed his watches so that he could put together sub-assemblies of about ten components each, and each sub-assembly could be put down without falling apart. Ten of these subassemblies could be put together to make a larger sub-assembly, and ten of the larger sub-assemblies constituted the whole watch."

Why do I blog this? This looks like a good way to introduce the notion of modularity, using an analogy which is understandable (as opposed to the use of fractals by other authors).