Interest rate is the effect, not the cause—at least in the evenly rotating economy ERE (ontologically). That is, the real income increase (in the sense of shifting of time preference schedule per se) doesn’t cause another round of saving—interest rates adjust immediately to reflect the shift of underlying time preferences in the economy, preventing recursive saving loops.

“Many economists have made the great mistake of believing that the interest rate determines the time-preference schedule and rate of savings, rather than vice versa.”

“The intersection of the two curves—supply of present goods and demand for present goods—determines the equilibrium rate of interest—the rate of interest as it would tend to be in the evenly rotating economy. This pure rate of interest is determined solely by the time preferences of the individuals in the society, and by no other factor.”

“It is this rate of interest that induces capitalists to save and invest present goods in productive factors.” (p. 403)

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