The Language Rules We Know – But Don’t Know We Know by Mark Forsyth
You are utterly familiar with the rule of ablaut reduplication. You’ve been using it all your life. It’s just that you’ve never heard of it. But if somebody said the words zag-zig, or ‘cross-criss you would know, deep down in your loins, that they were breaking a sacred rule of language. You just wouldn’t know which one.