According to simple Keynesian theory, the slope of the aggregate consumption curve against income is

According to simple Keynesian theory, the aggregate consumption function is expressed as C = a + cY, where 'a' represents autonomous consumption and 'c' represents the marginal propensity to consume (MPC) [1]. The slope of this consumption curve against income is defined by the MPC, which measures the change in consumption per unit change in income [2]. Keynesian theory posits that as income increases, consumption also increases, but by a smaller amount than the increase in income. This implies that the MPC is a positive value, typically between 0 and 1 [2]. Therefore, the consumption curve has a positive slope, indicating a direct relationship where higher income levels lead to higher aggregate consumption spending.

Sources

1. [1] Macroeconomics (NCERT class XII 2025 ed.) > Chapter 4: Determination of Income and Employment > 4.1.1. Consumption > p. 54
2. [2] Macroeconomics (NCERT class XII 2025 ed.) > Chapter 4: Determination of Income and Employment > Some Definitions > p. 55