Whoever gets the Democratic nomination, she or he will run in part on proposals to increase government spending. And you know what that will mean: There will be demands that the candidate explain how all this will be paid for. Many of those demands will be made in bad faith, from people who never ask the same questions about tax cuts. But there are some real questions about the fiscal side of a progressive agenda.

Well, I have some thoughts about that, inspired in part by looking at Elizabeth Warren’s proposals on both the tax and spending side. By the way, I don’t know whether Warren will or even should get the nomination. But she’s a major intellectual figure, and is pushing her party toward serious policy discussion in a way that will have huge influence whatever her personal trajectory.

In particular, Warren’s latest proposal on child care – and the instant pushback from the usual suspects – has me thinking that we could use a rough typology of spending proposals, classified by how they might be paid for. Specifically, let me suggest that there are three broad categories of progressive expenditure: investment, benefits enhancement, and major system overhaul, which need to be thought about differently from a fiscal point of view.

So, first off, investment – typically spending on infrastructure or research, but there may be some room at the margin for including spending on things like childhood development in the same category. The defining characteristic here is that it’s spending that will enhance society’s future productivity. How should we pay for that kind of outlay?