Robinson Crusoe lives on a desert island with Man Friday. There’s no need for money. But then Woman Saturday comes along, selling goods that both men want to acquire, and they devise the concept of money, which she quickly grabs the lions share of. Next, they discover a large village on the other side of the island. How does that change the value of their three-person economy when they introduce an island-wide currency? Then, when they find a neighbouring island with a very productive economy, what is their money worth now? Phil Dobbie takes Prof Steve Keen through a series of hypotheticals, to understand the role money plays, right from its origins.