 Subsequent developments in the new trade theory, motivated in part by the empirical shortcomings of the H–O model and its inability to explain intra-industry trade, have provided an explanation for aspects of trade that are not accounted for by comparative advantage.Nonetheless, economists like Alan Deardorff, Avinash Dixit, Gottfried Haberler, and Victor D. Norman have responded with weaker generalizations of the principle of comparative advantage, in which countries will only "tend" to export goods for which they have a comparative advantage.In both the Ricardian and H–O models, the comparative advantage theory is formulated for a 2 countries/2 commodities case.