All cultural products contain a mixture of two elements: conventions and inventions. Conventions are elements which are known to both the creator and his audience beforehand—they consist of things like favorite plots, stereotyped characters, accepted ideas, commonly known metaphors and other linguistic devices, etc. Inventions, on the other hand, are elements which are uniquely imagined by the creator, such as new kinds of characters, ideas, or linguistic forms.... Convention and invention have quite different cultural functions. Conventions represent familiar shared images and meanings and they assert an ongoing continuity of values; inventions confront us with a new perception of meaning which we have not realized before. Both these functions are important to culture. Conventions help maintain a culture's stability while inventions help it respond to changing circumstances and provide new information about the world.