(_b_) Closely related to this consideration, and working in with it at every point, is the question of the possibility of substituting another commodity for the one monopolised. This everywhere tempers the urgency of the need attaching to a commodity. There are few, if any, even among the commodities on which we habitually rely for food, shelter, clothing, which we could not and would not dispense with if prices rose very high. The incessant competition which is going on between different commodities which claim to satisfy some particular class of need cannot be got rid of by the monopoly of one of them. This is probably the chief explanation of the low prices of the Standard Oil. As an illuminant, oil is competing with gas, candles, electricity, and unless the monopoly were extended laterally so as to include these and any other possible illuminants, the Trust's prices cannot be determined merely by the pressure of the need for artificial light. Though to a modern society artificial light is probably even more important than sugar, a Sugar Trust may have a stronger monopoly and be able to raise prices higher than an Oil Trust, because the substitutes for sugar, such as molasses and beetroot, are less effective competitors than gas, candles, and electricity with oil. The power of railway monopolies largely depends upon the degree in which their services are indispensable, and no alternative mode of transport is open. Sometimes, however, they miscalculate the extent of their power. The high railway rates in England have recently led in several quarters to a substitution of road and canal traffic in the case of goods where rapidity of conveyance was not essential. So also in other cases sea-transport has been substituted. The stronger monopoly of American railways consists partly in the fact that distances are so great, and the sea-board or other water conveyance so remote, that over a large part of the Continent the monopoly is untempered by alternative possibilities of transport.