Fashion, fads and the popularity of choices: Micro-foundations for diffusion consumer theory

Knowledge acquisition by consumers is a key process in the diffusion of innovations. However, in standard theories of the representative agent, agents do not learn and innovations are adopted instantaneously. Here, we show that in a discrete choice model where utility-maximising agents with heterogenous preferences learn about products through peers, their stock of knowledge on products becomes heterogenous, fads and fashions arise, and transitivity in aggregate preferences is lost. Non-equilibrium path-dependent dynamics emerge, the representative agent exhibits behavioural rules different than individual agents, and aggregate utility cannot be optimised. Instead, an evolutionary theory of product innovation and diffusion emerges.