Is it farther or further?
In classical economic theory, the relation between these two factors determines the price of a commodity. This relationship is thought to be the driving force in a free market. As demand for an item increases, prices rise. When manufacturers respond to the price increase by producing a larger supply of that item, this increases competition and drives the price down. Modern economic theory proposes that many other factors affect price, including government regulations, monopolies, and modern techniques of marketing and advertising.