What Are the Constructive Theories of What Causes Inflation?

The conventional theory of what causes inflation is that too much money chasing not enough goods. But this explanation has both demand and supply elements to it, says Andrew Keen. There's a school of thought called monetarism which emphasized the money supply above all else. And so you could actually increase the money supply, but if that money isn't being spent, you could have a huge increase in the money supply without a huge rise in inflation.