20) Aggregation - Downward-sloping demand is faced by an industry as a whole or by a monopolist, and is characteristic of individual psychology. But when the part faces the whole, it is a price-taker and D=MR=AR=P on the horizontal plane. Downward-sloping curves added horizontally become flatter. Ambiguity reflecting the different points of view is one of the flimsiest features of the Neo-Classical model.