The article explores how different assets vary in how easily they can be turned into cash. Money is used because it's the most liquid asset, not because it has any special value. The model shows how economic activity and asset prices change when there are shocks to productivity and liquidity. It also looks at how government policies, like buying and selling assets, can affect the economy. This model focuses on liquidity, not fixed prices, and is inspired by older ideas from Keynes and Tobin.