In this posting, I will revisit the topic of analogies and explore how to create them. To begin creating an analogy, first reduce the target phenomenon to basic principles. Then find another, more familiar phenomenon with similar basic principles. In the preceding example of the bank bailout, the basic principles are a threat, caused by moral failure, that can spread unless actively opposed. It is common knowledge that fire is a threat that must be fought lest it spread, and that it can be caused by a moral failure such as malice or stupidity. In the example of electric current as water, the basic principle is something that flows. I’ve used another analogy to illustrate the movement positive charge carriers (“holes”) in semiconductor material. The basic principle is that when there’s a deficit of something, we sometimes “rob Peter to pay Paul,” that is, we fill the deficit at one location by creating a similar deficit in another location. The analogy I use is that of a tile puzzle, where a grid of square tiles with one empty space creates a numerical sequence or a picture until they are slid out of place, the object being to re-create the proper picture or sequence by sliding one tile into the empty space, thereby creating another empty space. What moves are the tiles or the electrons, but it’s easy to think of the process as “moving the hole.”

Another property to note regarding analogies is that not only can they be contrived, as in adding the “carelessness” proviso to the house fire analogy, those contrivances need not be possible in reality. This is an exercise of the imagination. In the previous post, “Levels of abstraction,” the analogy about the Russian dolls includes a provision that the innermost doll is the most detailed, even though that property is reversed in reality.