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vice versa. There is on this supposition no equation between the labour required in order to supply a certain quantity of x and the labour required to supply the quantity of y which is exchanged for that quantity of x. The quantities of labour, it should be remarked, must in the present section in strictness be conceived as measurable by an objective standard — so many foot-pounds, for example. But it is not easy, nor I think, usual, to treat economics proper with such abstract rigour, as entirely to keep out of sight the cognate proposition — strictly belonging to our Section II — that in the absence of mobility there will be no comparison between the trouble and benefit (in a subjective sense) resulting on an average to the parties on the different sides of the channel. On one side may be fruits growing wild, or quails rained from heaven, obtainable with a minimum of labour — with (practically) no labour at all if we suppose the amount of the commodity obtainable (per diem) to be limited. The denizens of this favoured island may be luxuriating in superfluity; while their customers have to toil hard in order to obtain the necessities of a miserable existence.
Though exchange without mobility may appear the simpler conception, it is not that which the classical writers have primarily entertained. To illustrate their conception of value dependent on and proportionate to quantity of labour, we may conceive regions which are at times islands, at times connected by dry land. The market is held, say at the time of high tide, and goes on much as we have already supposed. But it is no longer possible that any X should permanently fare worse than if he were to be transformed into a Y; since it is now open to him to transfer himself, at low tide, from one island to another. The passage between two islands may be more or less free; sometimes perhaps, only available at neap tides, so that a long period is required for a change in «market value» to lead to a change in «normal» value.
International Trade. — Exchange being the genus, and the absence of mobility the differentia of international trade; there is deducible from these essential attributes a characteristic property which may be enunciated as follows. The price1 of the commodities imported in (relation to) the
- I follow M. Walras in thus employing price in the more general sense of rate-of-exchange.