The economist Alex Tabarrok in a post today criticizes what he calls ”identity economics”. Tabarrok says: “Identity economics is bad economics”. By “identity economics,” he means a theory that jumps from an accounting identity to a claim about causation. Keynesian economics is a prime example of this fallacy, as Tabarrok’s quotation from Nick Rowe illustrates:
1. Y = C + I + G + X – M. Therefore an increase in Government spending will increase GDP.
2. Y = C + S + T. Therefore an increase in Taxes will increase GDP.
Takarrok summarizes:
My guess is that you are much more uncomfortable with the second of those two examples than the first. You have probably seen the first argument before, but have probably not seen the second. But they are both equally correct accounting identities and are both equally rubbish arguments.
Murray Rothbard long ago in Man, Economy, and State made the same point. He offered a reductio ad absurdum of the Keynesian multiplier:
"Social Income =Income of (insert name of any person, say the reader) + Income of everyone else, Let us use symbols:
Social income =Y
Income of the Reader=R
Income of everyone else =V
We find that V is a completely stable function of Y. . . .Let us say the equation arrived at is: V =.99999 Y Then, Y =.99999Y +R
.00001Y =R
Y=100,000 R.
This is the reader’s own personal multiplier, a far more powerful one than the investment multiplier. To increase social income and thereby cure depression and unemployment, it is only necessary for the government to print a certain number of dollars and give them to the reader of these lines.
