Five years ago, when my two sons were with their mothers, who worked for the UN Tribunal for Rwanda in Arusha and the AU in Addis Ababa, I decided to spend the December holidays reading about modern monetary theory (MMT), a new school of economic thought within the Keynesian tradition.

Spared of parenting duties and the dreaded school run, I read as much as I could. But I was none the wiser after a month, probably because most MMT economists are awful communicators. Over the next few years MMT began to make more sense as I read the work of great communicators such as Stephanie Kelton in the US and Frank Van Lerven in the UK. I am now a convert...