Ricardo's argument in favour of free trade has also been attacked by those who believe trade restriction can be necessary for the economic development of a nation. Utsa Patnaik claims that Ricardian theory of international trade contains a logical fallacy. Ricardo assumed that in both countries two goods are producible and actually are produced, but developed and underdeveloped countries often trade those goods which are not producible in their own country. In these cases, one cannot define which country has comparative advantage.