In section 18.2, Keynes briefly restates the key factors, and their causal relations, at play in the economy. He says that there will tend to be a natural inducement to invest, up to the point where investment causes the supply price to, in conjunction with the expectations around prospective yield, equilibrate such that the marginal efficiency of capital (i.e. the relation between the prospective yield and the supply price) reaches equality with the interest rate complex.
unresolved That said, I still do not know what this equality means exactly. Does this equilibrium mean that the cost of borrowing, for capital investment purposes, is roughly equal to, or slightly lower than, the net yield or profit obtained from the enterprise in which the capital is employed, within the maturity timeframe of the loan/bond in question?