Piketty is an economic illiterate

I have finally put my hands on a copy of Thomas Piketty’s Capital in the Twenty-First Century. And what do I find, that this world famous book, this book that is going to set our economic world on its head, in its introductory chapter makes a fundamental error in basic economic theory I would fail any first year student for making. Forget about fraudulent data. He has confused a shift in demand (ie a movement of the demand curve) with a change in quantity demanded (the effect on the number of units bought caused by a change in the price). For an economist, you cannot be more wrong than that. Here is the passage in which, of all things, he is discussing Ricardian land rents in a section he titles, “Ricardo: the principle of scarcity”:

“To be sure, there exists in principle a quite simple economic mechanism that should restore equilibrium to the process: the mechanism of supply and demand. If the supply of any good is insufficient, and its price is too high, then demand for that good should decrease, which should lead to a decline in its price.” (p.6 – my bolding)

He has here basically stated that insufficient supply (a shortage) will lead to a fall in price which you can see from the bits in bolding. An economist should immediately see the flaw, but for those not trained in the dark arts, let me explain.

1) The phrase, “if the supply of any good is insufficient” means, suppose there is more being demanded at the price than is being supplied. That is, suppose the price is below its equilibrium level so that there is upwards pressure on the price. He doesn’t say it quite that way, but only that “its price is too high” which, in theory terms, is a nonsense statement. But since he is talking about the pressure of demand on supply, he can only mean that the increase in demand is pushing the price up which is driving some people out of the market. As economists like to put it, the demand curve has moved to the right and prices have therefore gone up.

2) But because “its price is too high,” he writes, “then demand for that good should decrease.” Big, big mistake. He has shifted his meaning of “demand” from representing a movement of the entire demand curve to a movement along the demand curve. Higher prices, he is saying, cause the quantity demanded to fall. The demand curve stays put but with a higher price some people are leaving the market. That is why demand curves are downward sloping.

3) Then he writes that “demand for that good should decrease, which should lead to a decline in its price”. He has now mistaken a fall in quantity demanded, a movement along the curve, for a fall in demand, a movement of the entire curve to the left. He has confused a fall in the quantity demanded caused by a rising price with a fall in the level of demand, which is a shift of the entire curve.

This is one of the things I harangue my students about to stop them from making such elementary mistakes. Compare what Piketty wrote with the text of my Free Market Economics where I warn my students against making this absurd but common enough error, at least common enough amongst economic illiterates. From page 100:

Demand versus Quantity Demanded

People often do talk about demand as if it is a specific amount and it is therefore important to make sure that when someone is talking about “demand”, that one is aware of which meaning they have in mind.

Compare these two statements:

(1) if the price goes up demand goes down (and who would deny this is so?)

(2) if demand goes down the price goes down (and similarly, who would deny this?)

This becomes the following conclusion if the two statements are run together:

(3) if the price goes up [demand goes down; if demand goes down] the price goes down.

That is, if the price goes up the price goes down. A higher price is the cause of a lower price. Obvious nonsense, but it comes from using the word “demand” in its two different meanings.

In (1), this is using the word demand to mean a movement along the demand curve when the price happens to rise. In (2), this is using the word demand to mean a shift of the entire demand curve when one of the underlying factors has changed.

It is therefore essential to always make sure which meaning of demand is intended. You can usually tell from the context of what is being said, but the words here are slippery and can lead you into trouble.

This is trouble, all right. I find it absurd that Piketty cannot tell the difference between a shift of the demand curve and a movement along the demand curve.

To trust anyone’s economic judgment on serious economic matters who makes such a fundamental error would be ridiculous. He has 650 pages of stats and data but almost literally doesn’t know the first thing about economic theory?

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