There is also the old question of why mathematicians tend to prefer pencils over pens. The most common reason I've heard is to make correction easier, but I don

There is also the old question of why mathematicians tend to prefer pencils over pens. The most common reason I've heard is to make correction easier, but I don't think that's the real one. When I'm doing math, I never erase, I just cross out and work around it because it's just scratch paper anyway. I think the real reason for using pencil is the freedom to forget about it. With any type of pen, after a period of inaction, you have to fiddle a bit to get it writing nicely again. A pencil is instant, no matter how long you held it poised in air, pondering your next mark on the paper.