with its own environment; and his logical starting-point is an analysis of wealth-production as it exists to-day.  He begins by insisting on the fact that labour in the modern world is divided with such a general and such an increasing minuteness that each labour produces one kind of product only, of which he himself can consume but a small fraction, and often consumes nothing.  His own product, therefore, has for him the character of wealth only because he is able to exchange it for commodities of other kinds; and the amount of wealth represented by it depends upon what the quantity of other assorted commodities, which he can get in exchange for it, is.  What, then, is the common measure, in accordance with which, as a fact, one kind of commodity will exchange for any other, or any others?  For his answer to this question Marx goes to the orthodox economists of his time—­the recognised exponents of the system against which his own arguments were directed—­and notably, among these, to Ricardo; and, adopting Ricardo’s conclusions, as though they were axiomatic, he asserts that the measure of exchange between one class of commodities and another—­such, for example, as cigars, printed books, and chronometers—­is the amount of manual labour, estimated in terms of time, which is on an average necessary to the production of each of them.  His meaning in this respect is illustrated with pictorial vividness by his teaching with regard to the form in which the measure of exchange should embody itself.  This, he said, ought not to be gold or silver, but “labour-certificates,” which would indicate that whoever possessed them had laboured for so many hours in producing no matter what, and which would purchase anything else, or any quantity of anything else, representing an equal expenditure of labour of any other kind.

Having thus settled, as it seemed to him beyond dispute, that manual labour, estimated in terms of time, is the sole source and measure of economic values or of wealth, Marx goes on to point out that, by the improvement of industrial methods, labour in the modern world has been growing more and more productive, so that each labour-hour results in an increased yield of commodities.  Thus a man who a couple of centuries ago could have only just kept himself alive by the products of his entire labour-day, can now keep himself alive by the products of half or a quarter of it.  The products of the remainder of his labour-day are what Marx called a “surplus value,” meaning by this phrase all that output of wealth which is beyond what is practically necessary to keep the labourer alive.  But what, he asks, becomes of this surplus?  Does it go to the labourers who have produced it?  No, he replies.  On the contrary, as fast as it is produced, it is abstracted from the labourer in a manner, which he goes on to analyse, by the capitalist.