It was in virtue of this method, and by the light thrown by the type which he postulated, that Marx was able to discover and define the social origin of _profit_, _i.e._ of _surplus value_. Surplus value in pure economics is a meaningless word, as is evident from the term itself; since a _surplus value_ is an _extra value_, and thus falls outside the sphere of pure economics. But it rightly has meaning and is no absurdity, as a _concept of difference_, in comparing one economic society with another, one fact with another, or two hypotheses with one another. It is also in virtue of the same premise that he was able to arrive at the proposition: that the products of labour in a capitalist society do not sell, unless by exception, for their value, but usually for more or less, and sometimes with great deviations from their value; which is to say, to put it shortly, _value_ does not coincide with _price_. Suppose, by hypothesis the organisation of production were suddenly changed from a capitalist to a communistic system, we should see at once, not only that alteration in the fortunes of men which appeals so much to popular imagination, but also a more remarkable change: a change in the fortunes of things. A scale of valuation of goods would then fashion itself, very different for the most part, from that which now exists. The way in which Marx proves this proposition, by an analysis of the different components of the capital employed in different industries, _i.e._ of the proportion of fixed capital (machines, etc.) and of floating capital (wages), need not be explained here in detail. And, in the same way, _i.e._ by proving that fixed capital increases continually in comparison with floating capital, Marx tries to establish another law of capitalist society, the law of the _tendency of the rate of profits to fall_. Technical improvement, which in an abstract economic society would show itself in the decreased labour required to produce the same wealth, shows itself in capitalist society in a gradual decline in the rate of profits.[27] But this section of Volume III of _Das Kapital_ is one of the least developed in this little worked-out posthumous book; and it seems to me to be worth a special critical essay, which I hope to write at another time, not wishing to treat the subject here incidentally.[28] II MARX'S PROBLEM AND PURE ECONOMICS (GENERAL ECONOMIC SCIENCE) _Marxian economics not general economic science and labour-value not a general concept of value: Engel's rejection of general economic law: abstract concepts used by Marx are concepts of pure economics: relation of economic psychology to pure economics: pure economics does not destroy history or progress._