Classification for Dummies [Updated]

If you’ve ever wondered how idiots, morons and imbeciles rank against each other, this sample from an old book shows you:

So where does “dumbass” fit on this scale?

[Update: Here’s the source of the image — Better for All the World: The Secret History of Forced Sterilization and America’s Quest for Racial Purity, a book on the eugenics movement in the U.S. in the early 20th century.]