And, as with any self-respecting symbol, meaning is often packed into blackboard words to an unusually high degree. Lectures, primarily aural, are nonetheless calcified by these markings on the board; from their transcriptions students can often reconstruct entire verbal arguments. Blackboard scrawlings thus represent an extremely condensed language; no ordinary words, these can be extremely powerful in the context of memory.

For historical accuracy, the blackboard must be considered with all its variants--the overhead projector, the whiteboard, the large pad of paper, the PowerPoint presentation. But for reminiscence and generalization--for sheer metaphorical punch--the blackboard reigns supreme.

In that spirit of pedagogical curiosity--or of the needlessly patterning mind--here are "Thirteen Ways of Looking at a Blackboard":

1. Space which is perpetually too small to contain an entire idea.

2. As something waiting to be erased.

3. As something which has just been (imperfectly) erased.

4. The site of noisiest writing.