Gov. Brown and other advocates of a rainy day fund explain the concept as though it were simple. Put aside money in good times for a rainy day.

Then why don’t they just propose a rainy day fund?

By that I mean: why don’t they propose a rainy day fund that’s just a rainy day fund?

The two rainy day fund proposals before us – the one that’s on the ballot (though it keeps getting postponed) and Gov. Brown’s new proposal – have one big thing in common:

They’re not just rainy day funds. They actually do other things.

In the case of ACA 4, the ballot measure that dates to the Schwarzenegger governorship, the rainy day fund reflects a desire to limit spending long-term, via a 20-year estimate of spending so exotic that the data required to make it work does not currently exist, according to the legislative analyst’s office. The ACA4 rainy day fund also includes provisions that would send certain moneys to infrastructure – instead of into a reserve fund.

Governor Brown’s rainy day fund proposal isn’t clean either. It enhances the powers of the governor in budget emergencies. It also provides complicated new applications of the Proposition 98 school funding guarantee, including a rainy day fund for Prop 98 within the largest rainy day fund. The Brown proposal also favors paying down debt, paying for infrastructure, and covering pension and retiree health benefits over saving money for a rainy day, at least in certain circumstances.

If you wanted to be cynical – which I wouldn’t dare be in this space – you might say that politicians of both parties use the popular notion of rainy day funds as cover to advantage certain kinds of spending in budget formulas.

A cynic might also say that the rainy day fund proposals create reserves that are too small to have covered much of the budget cuts in the past decade.

And the truly dark-hearted might point out that California already has two rainy-day funds, but that no one uses them.

But, please. These reserve fund proposals are very simple, and just about putting money away for rainy days.