A2 Revision: The Perfectly Competitive Firm and the Market
Supernormal, normal, and subnormal profit only identified what happens to the firm. However it is important to be aware of what is happening in the market as a whole. Take for instance a firm making supernormal profits. The price that the firm charges is determined by what is happening in the market (supply and demand). If a firm makes supernormal profits this attracts other firms into the industry to take advantage of these profits. Therefore the supply of firms in the market increases which in turn reduces the price that firms can charge and they now make normal profits and are in the long-run see fig below.