This document discusses three concepts related to consumer demand theory: the bandwagon effect, snob effect, and Veblen effect. The bandwagon effect refers to how consumer demand for a product increases when others are also consuming it. The snob effect is the reverse, where demand decreases when a product becomes too mainstream. The Veblen effect means demand increases when a product's price is higher, as it signals wealth and status. The document proposes incorporating these effects into demand theory by accounting for interpersonal utility factors like social influence, exclusivity desires, and conspicuous consumption. It suggests demand curves may not represent simple individual preferences due to these external consumption effects.