Neoclassical textbooks define a firm acting without any strategic awareness of the effect of its output choice on price as representing "perfect competition" and argue that this condition of "perfect competition" can be represented analytically by a horizontal demand curve facing the firm -- the firm acts as if it believes it can sell whatever it produces at the currently prevailing price, but nothing at any higher price; marginal costs for this firm, it is presumed, are rising and the firm does not want to sell more at the current price or a lower price.