J. Scott Applewhite / AP Senate Majority Leader Harry Reid

Fact: I do not know whether Mitt Romney paid federal income taxes, when, or how much, in any year before 2010, for which he publicly released his tax returns. Fact: You probably do not either, unless you are among the small army of spreadsheet-slinging professionals it must take to shepherd his wealth, or—possibly—if you are Mitt Romney.

Fact: Sen. Harry Reid is also not in a position to know definitively whether and how much tax Romney has paid, though that has not stopped him claiming–and claiming, and re-claiming–that someone in a position to know told him Romney paid no income tax for ten years. And fact: the watchdog fact-checking outlet PolitiFact assigned Reid its dreaded “Pants on Fire” label for said claim, although, fact: PolitiFact does not and cannot know either whether it is true or false.

OK, first, let me deal with what I’m not going to argue in this post: the fairness of Reid’s claim, its plausibility, the seriousness with which anyone should take it without evidence, the political strategy behind it, Romney and Reid’s relative credibility, the fact that Romney could address the question by releasing his tax returns, the political strategy behind this choice, or what all this says about who should be elected President in November. There are many fine places on the Internet to heartily debate these matters. Go to one of them!

What I’m interested in here is that if you call someone a liar, you’ve got to show them lying. It endangers PolitiFact’s hard-earned and important position as referee in the mudslinging contest–a “truth vigilante,” as it were–for it to call someone a liar on the basis of something that may or may not be false. Reid’s charges are unsubstantiated, not backed up and at best hearsay. But his basic charge–that someone told him Romney did not pay taxes–may well be true even if Romney did pay. PolitiFact ruled “Pants on Fire” on the basis that Reid did not prove his charge, meaning that it is now possible to get called a liar by PolitiFact for saying something true.

Now, fact: PolitiFact has defended itself, saying it never used the word “lie.” Rating: True, but! As long as PolitiFact is policing inferences and insinuations, any idiomatic American English speaker should know that there is one act that metaphorically sets one’s trousers ablaze, and if PolitiFact does not know what that is, I question whether America’s kindergartens are doing their job.

That said, I get what PolitiFact is trying to do, and why it needs to try to do it. If big political lies were all easily empirically dispelled, we wouldn’t need PolitiFact at all. Dishonesty is much more flexible than that. Where a baldfaced lie won’t fly, you can spin, shade the truth, insinuate, use logical fallacies, rely on dubious subjective interpretations or make insinuations–“A guy told me this thing, who knows?”–that will later get spread as truth.

Those are as dangerous, if not more so, as blatant falsehoods of fact, and they’re tougher to deal with. The Reid statement is not like the claim that Barack Obama was born in Kenya, for which there is direct and concrete documentation to cite to the contrary. It’s a formless whisper–I heard it from a guy–and, yeah, it can do all kinds of damage for this kind of thing to go on unchallenged. (And without judging what’s equivalent to what, any Obama supporters defending Reid should at least keep in mind all the things someone has “heard from a guy” about Obama for the last four years.)

So I get why PolitiFact needs to address this stuff too. And why it may seem nitpicky for them to accuse Reid of lying–sorry, setting his pants on fire–when what they really mean is something harder to sum up in a catchphrase: that he’s willfully rumormongering, trying to spread an impression that is at worst completely bogus and at best he has given no evidence for. (Brendan Nyhan at CJR has a good post about why PolitiFact critics should not let Reid off the hook.)

But the whole reason that PolitiFact exists is that words and facts matter. PolitiFact’s job is important because inaccurate-but-catchy language, deployed a certain way and repeated, can create false impressions and misinform people. So it is with “Pants on Fire” here. To an average listener, PolitiFact is not saying that Reid has made a statement he can’t prove. They’re saying that he’s made a statement that is actually false–and thus, they seem to certify that Romney has in fact paid taxes for years in which we don’t know one way or another.

I believe PolitiFact is trying to do the right thing here. And despite the efforts of partisans to work the refs by complaining about various calls they’ve made in the past, they’re generally doing a hard, important thing well. They often do it better than the rest of the political media, and the political press owes them for doing it.

But if their rating system–designed, ironically, to abet the truth by making it as easy to spread via catchphrase as a lie–is sending false messages, then they need to improve their rating system, to address the irresponsible, the unprovable, the dubious. Otherwise, they’re doing exactly what they were founded to stop: using language to spread false impressions. You can tell them a guy told you that about them.