Joe Biden, in his role as self-appointed media critic for last night’s Democratic debate, apologized after answering a question about Pakistan. “I know you’re not supposed to answer questions, based on what I’ve heard,” he quipped.

That imperative—as in, ‘it’s imperative that candidates be as vague as possible on complex and/or divisive issues’—has been evident in each debate. But it was particularly evident last night. As The New York Times’s Katherine Seelye asked in her live-blogged debate coverage:

Is anyone besides us more confused than ever? Universal health care, driver’s licenses for undocumented residents, merit pay for teachers … the answers are so swathed in verbiage that it’s hard to say what some of these candidates would actually do.

Amen to that. For all the grandiose talk of debate questions being of/by/for “the people,” their answers often benefit only the candidates themselves, buying them time before they really have to commit to a stance on a given issue. And the media, who are supposed to be un-spinning the spin, are often the ones who let them get away with it.

The term “merit pay,” as Seelye singled out in her litany against “verbiage,” is a perfect example of this kind of semantic obfuscation. It’s a loaded and somewhat confusing term—which, to his credit, CNN’s John Roberts tried to explain last night as he asked the candidates about education:

In workplaces across America, it’s pretty common practice to reward high-performing employees with pay raises, and to terminate bad employees. However in our education system across the country, by and large in our nation’s public schools, teachers unions make it difficult to do that.

The question is, what is wrong with rewarding a teacher who excels at the job that they’re doing by paying them more than an average teacher would make? (Applause.)

So Roberts takes a first step—highlighting the fact that there’s a connection between merit pay and teachers’ unions—but the connection itself is still unclear. How do the unions “make it difficult” to reward the high performers and fire the low? Roberts never says.

Nor does Wolf Blitzer, in his own question on education:

We’re talking about education right now, and I want to bring Congressman Kucinich in because I know you’re a strong supporter of the unions. The teachers’ union, very powerful—teachers’ unions, very powerful. Are there any issues with unions—teachers’ unions, or other unions for that matter—with which you disagree?

Fair enough. What the Vegas questioners leave out, though—and it’s a crucial piece of information to know in order to assess candidates’ answers—is the connection between part 1 (merit pay) and part 2 (teachers’ unions). “Merit pay,” after all, sounds like the most obvious and intuitive thing in the world: do a good job, get paid for it. Do a better job, get paid better. Do a lousy job, face the consequences. Easy enough, right? But here’s the thing: to advocate ‘merit pay’ is essentially to position oneself against one of the Democrats’ core constituencies: teachers’ unions.

Most collectively-bargained teaching contracts, as they currently stand—and they stand that way because their members want them to—base teachers’ pay raises on tenure. So new teachers get horrible pay; more experienced teachers get slightly-less-horrible pay. That’s regardless of teachers’ individual performances (measured, usually—and even before No Child Left Behind—by their students’ test scores). Furthermore, the way most contracts are currently set up—though some school districts are chipping away at changes—underperforming teachers are nearly impossible to fire.

This tenure-based pay system leaves room for the type of situation Blitzer brought up last night in response to Clinton’s claim that she supports school-based merit pay:

Well, what if there’s an excellent teacher in that team and a crummy teacher in that team, a teacher who’s simply riding along and not really working very hard, not really educating those young kids? Do you give just everybody the merit pay, or do you give the individual teacher?

Here’s Clinton’s answer:

Wolf, you need to weed out the teachers who are not doing a good job. I mean, that’s the bottom line. (Applause.) They should not be teaching our children.

And how did the candidates, overall, respond to the merit-pay-for-individual-teachers line of questioning?

• Biden: unclear (“I believe there should be teaching excellence.”)

• Clinton: unclear (“I support school-based merit pay….We need to get more teachers to go into hard-to-serve areas.”)

• Dodd: against (“If you define excelling by teachers who will go into poor rural or poor urban areas and make a difference…then I think that sort of merit pay has value. If you’re judging excelling by determining whether or not that teacher has students who do better because they’re in better neighborhoods or better schools, I’m totally opposed to that.”)

• Edwards: [not asked]

Megan Garber is an assistant editor at the Nieman Journalism Lab at Harvard University. She was formerly a CJR staff writer.