Lewis tried to elucidate the capital accumulation problem of a dual economy characterized by co-existence of a pre-capitalistic agricultural sector and a capitalistic industrial sector. However, the lack of his consideration on the change in the terms of trade between these sectors made it impossible to state in a satisfactory form the condition for "take-off" and sustained growth.
Even after Lewis' work, due attention has not been paid to effects on "take-off" of the capital accumulation in the pre-capitalistic agricultural sector.
This paper pays regard to the neglected factors and presents the Critical Minimum Effort Criterion for "take-off". The conclusions are as follows.
(1) Whether the economy is dual or mature depends on the ratio of the capital in the agricultural sector to total labor population.
(2) Suppose the economy is dual at a starting point. Further, suppose long-run equi-libria exist (the condition for existence of them is presented). Then, if the ratio of the capital in each sector to total labor population is over the critical level, the agricultural sector becomes capitalistic and the economy converges asymptotically to a long-run equilibrium in a mature economy. If not, the economy tends to a traditional agrarian economy in which the capitalistic industrial sector cannot exist.
Conversely, unless long-run equilibria exist, there is no possibility of economic development and the economy tends to a traditional agrarian economy. Therefore, in this case, the reform of the structure by introducing high-productive technic into each sector or by reducing the growth rate of labor population is the first consideration for economic development
