1) Accelerator theory of investment: This theory suggests that the level of investment is directly related to the rate of change in the level of economic output. In other words, when the economy is growing rapidly, businesses are more likely to invest in new capital goods to meet the increasing demand. Conversely, during periods of economic downturn, investment tends to decrease as businesses are less confident in the potential return on investment.
2) The classical theory of economic growth: The classical theory of economic growth, also known as the neoclassical growth theory, emphasizes the role of technological progress and capital accumulation in driving long-term economic growth. According to this theory, an increase in the capital stock, through investment in new machinery, equipment, and infrastructure, leads to higher levels of output and income. Technological progress is seen as a key driver of economic growth, as it allows for more efficient production methods and the development of new goods and services.