the merchant had observed that the marginal utility of daughters decreases with surprising rapidity. - Joan Robinson

An agent must have some discretion.

Marx, however imperfectly he worked out the details, set himself the task of discovering the law of motion of capitalism, and if there is any hope of progress in economics at all, it must be in using academic methods to solve the problems posed by Marx.

It seems that neither the Keynesian nor the Marxian prognosis of the future of capitalism is being fulfilled and we are left without any particular theory as to what will happen next.