Now, whatever may be the value of such teaching as a contribution to economic science, it illustrates by its success one cardinal truth, and by implication it bears witness to another. The first truth is that, no matter how desirable any object may be which is obtruded on the imagination of anybody, nobody will bestir himself in a practical way to demand it until he can be persuaded to believe that its attainment is practically possible. The other is this: that the possibilities of redistributing wealth depend on the causes by which wealth is produced. All wealth, says Marx, can practically be appropriated by the labourers. But why? Because the labourers themselves comprise in their own labour all the forces that produce it. If its production necessitated the activity of any persons other than themselves, these other persons would inevitably have some control over its distribution; since if it were distributed in a manner of which these other persons disapproved, it would be open to them to refuse to take part in its production any longer; and there would, in consequence, be no wealth, or less wealth, to distribute. Let us, then, examine the precise sense and manner in which this theory of labour as the sole producer of wealth is elaborated and defended by Marx in his Bible of Scientific Socialism. His argument, though the expression of it is very often pedantic and encumbered with superfluous mathematical formulae, is ingenious and interesting, and is associated with historical criticism which, in spite of its defects, is valuable. Marx was, indeed, foremost among those thinkers already referred to who first insisted on the fact that the economic conditions of to-day are mainly a novel development of others which went before them, and that, having their roots in history, they must be studied by the historical method. He recognised, however, that for practical purposes each age must concern itself 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,