The second essential element of a cap and trade scheme is the ability to trade. Since carbon pollution permits will be tradable, the price of permits will be determined by the market (Department of Climate Change, 2008, 13). The main idea behind this part of the scheme is that a firm who can undertake abatement more cheaply than the permit price will do so, and that a company will pay for permits if the cost to it of lowering its emissions exceeds the cost of the permits. By trading among themselves, firms achieve the scheme cap at the least cost to the economy (Department of Climate Change, 2008, 13).