In contrast to the production-side argument, the "consumption-side" theory of urban gentrification posits that the "socio-cultural characteristics and motives" of the gentrifiers are most important to understanding the gentrification of the "post-industrial city". The changes in the structure of advanced capitalist cities with the shift from industrial to service-based economy were coupled with the expanding of a new middle class—one with a larger purchasing power than ever before. As such, human geographer David Ley posits a rehabilitated post-industrial city influenced by this "new middle class". The consumption theory contends that it is the demographics and consumption patterns of this "new middle class" that is responsible for gentrification.