Editor's note: Originally published at tsi-blog.com on October 18, 2016
All else remaining equal, an increase in the supply of money will lead to a decrease in the purchasing power (price) of money. Furthermore, this is the only effect of monetary inflation that the average economist or central banker cares about. Increases in the money supply are, therefore, generally considered to be harmless or even beneficial as long as the purchasing power of money is perceived to be fairly stable*. However, reduced purchasing power for money is not the most important adverse effect of monetary inflation.
If an increase in the supply of money led to a proportional shift in prices throughout the economy then its consequences would be both easy to see and not particularly troublesome. Unfortunately, that's not the way it happens. What actually happens is that monetary inflation causes changes in relative prices, with the spending of the first recipients of the newly-created money determining the prices that rise the first and the most.
Changes in relative prices generate signals that direct investment. The further these signals are from reality, that is, the more these signals are distorted by the creation of new money, the more investing errors there will be and the less productive the economy will become.
Also, although adding to the money supply cannot possibly increase the economy-wide level of savings, monetary inflation temporarily creates the impression that there are more savings than is actually the case. This reduces interest rates, which prompts investments in ventures that are predicated on unrealistic forecasts of future consumer spending. Again, the eventual result will be a less productive economy.
During any given year, it usually won't be possible to separate out the pernicious effects of monetary inflation and the distortion of interest rates that goes hand-in-hand with it from all the other forces affecting the economy. There will simply be too many things going on in the world that could be influencing the data. However, by taking a wide-angle (that is, long term) view it will often be possible to see the effects on the economy of shifts in monetary inflation.
As an example of how long-term shifts in monetary inflation/intervention can be linked to long-term shifts in economic progress, I present the following chart of the US Industrial Production Index. The chart shows that the industrial-production growth trend flattened at around the time that the 'golden shackles' were removed, that is, at around the time that the Fed was essentially empowered to do a lot more. This is not a fluke. The chart also shows that the ramping up of the Fed's monetary interventions in 2008-2009 has been followed by the weakest post-recession recovery in at least 70 years. Again, this is not a fluke.
In economics, to have a chance of correctly interpreting cause and effect in the data, you first have to know the right theory. That's why Keynesian economists will not link the US industrial production slowdown with the Fed's increasingly aggressive monetary interventions. From their perspective, the only negative effect that monetary inflation can possibly have is to make the cost of living rise at a faster pace than they believe it should be rising.
*Stable, here, means rising at around 2% per year. Note that it is not possible to come up with a single number that represents the economy-wide purchasing power of money, but this doesn't stop the government (and some private organisations and individuals) from doing exactly that.