(NYTIMES) - The world is complicated, and our minds have limited capacity, so we create categories to help us make sense of things. We divide, say, the social world into types - hipster, evangelical, nerd, white or black - and associate traits or characteristics with each.

These judgments involve simplifications and generalisations. But we couldn't make sense of the blizzard of sensory data each day if we couldn't put things, situations and people into some form of conceptual boxes.