The gross substitution axiom — the backbone of mainstream economics

15 Aug, 2014 at 19:59 | Posted in Economics | 4 Comments

The gross substitution axiom assumes that if the demand for good x goes up, its relative price will rise, inducing demand to spill over to the now relatively cheaper substitute good y. For an economist to deny this ‘universal truth’ of gross substitutability between objects of demand is revolutionary heresy – and as in the days of the Inquisition, the modern-day College of Cardinals of mainstream economics destroys all non-believers, if not by burning them at the stake, then by banishing them from the mainstream professional journals. Yet in Keynes’s (1936, ch. 17) analysis ‘The Essential Properties of Interest and Money’ require that:

1. The elasticity of production of liquid assets including money is approximately zero. This means that private entrepreneurs cannot produce more of these assets by hiring more workers if the demand for liquid assets increases. In other words, liquid assets are not producible by private entrepreneurs’ hiring of additional workers; this means that money (and other liquid assets) do not grow on trees.

2. The elasticity of substitution between all liquid assets, including money (which are not reproducible by labour in the private sector) and producibles (in the private sector), is zero or negligible. Accordingly, when the price of money increases, people will not substitute the purchase of the products of industry for their demand for money for liquidity (savings) purposes.

These two elasticity properties that Keynes believed are essential to the concepts of money and liquidity mean that a basic axiom of Keynes’s logical framework is that non- producible assets that can be used to store savings are not gross substitutes for producible assets in savers’ portfolios. If this elasticity of substitution between liquid assets and the products of industry is significantly different from zero (if the gross substitution axiom is ubiquitously true), then even if savers attempt to use non-reproducible assets for storing their increments of wealth, this increase in demand will increase the price of non- producibles. This relative price rise in non-producibles will, under the gross substitution axiom, induce savers to substitute reproducible durables for non-producibles in their wealth holdings and therefore non-producibles will not be, in Hahn’s terminology, ‘ultimate resting places for savings’. The gross substitution axiom therefore restores Say’s Law and denies the logical possibility of involuntary unemployment.

Paul Davidson