is necessary to sustain society at a given living standard (a surplus product); the additional product-value is available for investments which enlarge the scale and variety of production. The bourgeois claim there is no economic law according to which capital is necessarily re-invested in the expansion of production, that such depends on anticipated profitability, market expectations and perceptions of investment risk. Such statements only explain the subjective experiences of investors and ignore the objective realities which would influence such opinions. As Marx states in Vol.2, simple reproduction only exists if the variable and surplus capital realized by Dept. 1—producers of means of production—exactly equals that of the constant capital of Dept. 2, producers of articles of consumption (pg 524). Such equilibrium rests on various assumptions, such as a constant labor supply (no population growth). Accumulation does not imply a necessary change in total magnitude of value produced but can simply refer to a change in the composition of an industry (pg. 514). Ernest Mandel introduced the additional concept of contracted economic reproduction, i.e. reduced accumulation where business operating at a loss outnumbers growing business, or economic reproduction on a decreasing scale, for example due to wars, natural disasters or devalorisation. Balanced economic growth requires that different factors in the accumulation process expand in appropriate proportions. But markets themselves cannot spontaneously create that balance, in fact what drives business activity is precisely the imbalances between supply and demand: inequality is the motor of growth. This partly explains why the worldwide pattern of economic growth is very uneven and unequal, even although markets have existed almost everywhere for a very long time. Some people argue that it also explains government regulation of market trade and protectionism. Origins According to Marx, capital accumulation has a double origin, namely in trade and in expropriation, both of a legal or illegal kind. The reason is that a stock of capital can be increased through a process of exchange or "trading up" but also through directly taking an asset or resource from someone else, without compensation. David Harvey calls this accumulation by dispossession. Marx does not discuss gifts and grants as a source of capital accumulation, nor does he analyze taxation in detail (he could not, as he died even before completing his major book, Das Kapital). Nowadays the tax take is often so large (i.e., 25-40% of GDP) that some authors refer to state capitalism.