Krugman is on crack, or I'm very confused. He writes: "As a matter of simple arithmetic, total spending in the economy is necessarily equal to total income (every sale is also a purchase, and vice versa). So if people decide to spend less on investment goods, doesn't that mean that they must be deciding to spend more on consumption goods—implying that an investment slump should always be accompanied by a corresponding consumption boom?"

This plainly assumes spending is constant in a deep recession. I thought a recession is pretty much defined by significantly lower spending. What am I missing?