There is, indeed, no formula in political economy on which the modern economist looks with more suspicion than that of Supply and Demand. The operation of supply and demand as determining market price is, of course, perfectly definite; but to say that any concrete price is fixed by the equation of supply and demand is a mere statement of an observed fact which says little, unless one knows and defines accurately what is involved in the "supply," what is involved in the "demand," and how those two factors stand related to each other. The price of railway stock to-day is determined by supply and demand; the price of a man's labour, whether unattached or working under restriction of the Trade Union, is determined by supply and demand; the earnings of the poor soul who sells her body on the streets are determined by supply and demand. What does this formula tell us unless we know the complex phenomena which determine the supply of railways and the demand for transit, the supply of labourers and the demand for work, the supply of hapless women and the demand for human souls? To say, then, that women's wages are low because there are enough women who take the low wage, is little more than to say that wages are low because people are paid low wages. We have still to ask: What are the factors, or influences, or motives, that make women take a wage below that of men, and what are the factors that make employers offer the low wage? Apart from the general insufficiency of this first answer, it is enough to remember that the determination of wage by this mechanical equation of supply and demand could be tolerable only under absolutely free competition, which would involve perfect mobility of labour. But labour has this unique characteristic among all commodities that, physically, it is not mobile; historically, it has never been mobile; and ethically, it should not be mobile. A man's labour is--and should be--his life, not the mere instrument of providing a living; and, therefore, in the question of wages it is impossible to ignore the ethical consideration. Civilised society could not hold together if the workman and workwoman could only get their fair share of the world's boundless wealth by changing their trade, their residence, or their country, as a higher wage offered itself.