THE other day my brother-in-law came back from a week-long family vacation in Maine, where he had visited a salt-water taffy museum, and announced he had learned something new: the secret ingredient in salt-water taffy. "It's marshmallow fluff," he explained. This, I felt, was a classic case of begging the question. (Anyone who knows what marshmallow fluff is made of, feel free to respond in comments.) And I felt rather the same way later that day, when I heard Mitt Romney had announced he had picked Paul Ryan as his running-mate.

Mr Romney had faced a week of withering criticism over the opacity of his budget plans, touched off by the Tax Policy Center's finding that any plan which could meet his vague, largely numbers-free promises would require large tax increases on the middle class. Mr Romney's spokespeople attacked that report for failing to use the candidate's own specific tax and spending proposals, but were unable to explain what those proposals are, because they don't exist. The selection of Mr Ryan was quickly applauded as a move to lend substance and specificity to Mr Romney's maddeningly content-free campaign. You want specific spending cuts and tax-preference eliminations, Mr Romney was saying—talk to the man who wrote the plan, Paul Ryan himself!

The problem here is pretty clear. For the past year and a half, Mr Ryan has been subjected to the very same criticism leveled at Mr Romney: that he refuses to specify the spending cuts and tax-preference eliminations his budget plan would make in order to meet its deficit targets. In March, the Congressional Budget Office analysis of Mr Ryan's most recent proposals noted that Mr Ryan had failed to explain how his budget could possibly cut the entire federal budget apart from Social Security, Medicare and Medicaid from 12.5% of GDP today to 5.75% of GDP by 2030. More recently, Peter Orszag writes that Mr Ryan's estimates of future Medicaid savings are unrealistic fantasies. David Stockman, the wild-eyed leftist radical who ran Ronald Reagan's budget, calls Mr Ryan's plan "devoid of credible math or hard policy choices". And so on. In short, if Mr Romney's budget plan is the salt-water taffy here, Mr Ryan's is the marshmallow fluff. You don't get any more concrete by saying that Mr Romney's budget proposals are comprised of Mr Ryan's, any more than you get more concrete by saying taffy is made of fluff, or that fire is made of phlogiston, or that the planets move because they have the property of movement. All you're doing is stringing the voter along in a never-ending philosophical subterfuge, a dance of the seven veils that continues forever but where nobody ever ends up naked.

Jacob Weisberg disagrees; he thinks liberal efforts to portray Mr Ryan as a "humbug" who won't specify the measures he wants to take are off the mark.