Harvey Leibenstein’s Critical Minimum Effort Thesis is an important theory of economic development that explains why many developing countries remain trapped in a condition of low income, low productivity, and slow economic growth. The theory was developed by the economist Harvey Leibenstein, particularly in his work on economic backwardness and development. It focuses on the interaction between population growth, income growth, investment, productivity, and the forces that either promote or obstruct development. According to Leibenstein, a developing economy must make a sufficiently large and sustained development effort to cross a certain minimum threshold. If the effort remains below this critical level, the economy tends to return to a low-level equilibrium, while an effort above the critical minimum can set the economy on a path of sustained growth. The basic idea behind the thesis is that development does not necessarily occur automatically through small and gradual increases in income. In poor economies, an increase in income may generate forces that counteract the benefits of economic growth. One of the most important of these forces is population growth. When per capita income rises slightly above the subsistence level, mortality tends to decline because people have better access to food, sanitation, and basic health services. However, fertility may remain high for some time. As a result, population increases rapidly. The additional population absorbs much of the increase in national income, causing per capita income to fall back toward the subsistence level. Leibenstein therefore distinguished between forces that encourage population growth and forces that contribute to economic growth. He described certain factors as “income-depressing” and “income-generating” factors. Income-depressing factors include rapid population growth, diminishing returns to factors of production, and other conditions that reduce the effect of increases in national output on per capita income. Income-generating factors include investment, technological progress, improvements in skills, better organization, and increased productivity. The central concept in the theory is the “critical minimum effort.” This refers to the minimum level of investment and development effort required to move an economy from a low-level equilibrium to a sustained growth path. If development efforts are too small, they may be neutralized by population growth and other obstacles. In such a situation, per capita income may increase temporarily but eventually decline again. If the development effort is sufficiently large, however, income can rise faster than population and create conditions favourable to continuous economic expansion. The theory can be understood through the concept of a poverty trap. In a poor country, low income leads to low savings and low investment. Low investment results