Four kinds of people

There are four kinds of people in this world: cretins, fools, morons, and lunatics…

Cretins don’t even talk; they sort of slobber and stumble…

Fools are in great demand, especially on social occasions. They embarrass everyone but provide material for conversation…Fools don’t claim that cats bark, but they talk about cats when everyone else is talking about dogs. They offend all the rules of conversation, and when they really offend, they’re magnificent…

Morons never do the wrong thing. They get their reasoning wrong. Like the fellow who says that all dogs are pets and all dogs bark, and cats are pets, too, therefore cats bark…Morons will occasionally say something that’s right, but they say it for the wrong reason…

A lunatic is easily recognized. He is a moron who doesn’t know the ropes. The moron proves his thesis; he has logic, however twisted it may be. The lunatic on the other hand, doesn’t concern himself at all with logic; he works by short circuits. For him, everything proves everything else. The lunatic is all idée fixe, and whatever he comes across confirms his lunacy. You can tell him by the liberties he takes with common sense, by his flashes of inspiration, and by the fact that sooner or later he brings up the Templars…There are lunatics who don’t bring up the Templars, but those who do are the most insidious. At first they seem normal, then all of a sudden…

― Umberto Eco, Foucault's Pendulum