anything from the origins of trade itself, not limited to the capitalist mode of production, to the origins of significant international wage-differentials, or to the post-war appearance of a significant net-inflow of raw-materials to the developed countries. In the approach of Immanuel Wallerstein the origins of the modern world-system, or what others, such as Ernest Mandel, would call the rise of merchant capitalism, is said to have entailed unequal exchange, although the idea was criticised by Robert Brenner. Another aspect of these theories is the criticism of fundamental assumptions of Ricardian and neoclassical theories of comparative advantage, which could be taken to imply that international trade would have the effect of equalising the economic position of the trading partners. More generally, the concept was a criticism of the idea that the operation of markets would have egalitarian effects, rather than accentuating the market position of the strong and disadvantaging the weak. Modern liberal economists work under the assumption that value is essentially a question of style, moral behavior and the spirituality of individuals, not an economic issue. If unfair trading practices occur, it must be that there is an impediment to freely competitive markets; and if those markets or market access could be open, all would be fair. Marxian economists, on the other hand, argue that the cheap labor found in undeveloped economies allows for profit which would not be possible where wages are higher. Raul Prebisch and Hans Singer hypothesized that the price of raw materials declines relative to finished industrial products. This makes "peripheral" countries rich in resources tend towards less power in trade. In Marxian economics Karl Marx aimed to go beyond moral discussion, in order to establish what, objectively speaking, real values are, how they are established, and what the objective regulating principles of trade are, basing himself principally on the insights of Adam Smith and David Ricardo (but many other classical political economists as well). He was no longer immediately concerned with what a "morally justified price" is, but rather with what "objective economic value" is, such as is established in real market activity and real trading practices. Marx's answer is that "real value" is essentially the normal labour cost involved in producing it, its real production cost, measured in units of labour time or in cost-prices. Marx argues that the "real values" in a capitalist economy take the form of prices of production, defined