How do we know who's a papal contender?

On Monday, I was catching my breath between bits of TV commentary, standing at a coffee bar with some colleagues, one of whom had just filed the usual story about who's in contention for the papacy. He relayed the reaction of his editor, which drew a deep laugh from all: "What's the source for this?"

We laughed not because it's an illegitimate question. Obviously, the journalistic ideal is to back up every assertion by citing named sources, allowing the reader or viewer to evaluate their credibility.

The laugh was because we know conclave coverage always falls well short of that ideal. Cardinals do not speak on the record about who might get their vote, so by definition, the usual sourcing protocols are out the window.

Still, the question deserves an answer: How do we know that the names we've been tossing around, such as Angelo Scola, Marc Ouellet and Odilo Pedro Scherer, really are in contention?

In my experience, it's a combination of three things.

First are background conversations with cardinals themselves. If you've developed relationships with members of the college over the years, they're sometimes willing, on background, to offer a reality check -- to confirm a figure is actually drawing consideration or to quietly suggest you look elsewhere. Prior to moving into the Casa Santa Marta on Tuesday morning, cardinals have remained available for these insights, though they're not delivering them in full public view.

Second are the reports of other journalists, who are having the same conversations with their own sources. Over time, one learns which bylines to trust: which reporters have the best connections and are most on the money in knowing which way the winds are blowing. Such history doesn't make anyone infallible, but it does provide a useful filter for separating the wheat from the chaff.

Third, one listens carefully to what the cardinals are saying about the qualities the next pope needs to have, then matches those descriptions against their profiles. If you hear certain qualities clearly associated with a certain figure popping up over and over again, that's a good sign his candidacy has some legs.

In other words, discerning the papabili is a combination of old-fashioned reporting and reading the tea leaves. It's a speculative enterprise, but in the right hands, it's more than throwing a dart at a board.

For confirmation of the point, Chicago Cardinal Francis George said in a March 2 interview with NCR that "the names out there, I've found, are all reasonable candidates ... This time the names that are before us in the public media are, in fact, serious candidates."

George also said there may be some candidates who haven't popped up on the media radar screen, but his comments at least suggest the names floating through the Roman air are indeed likely to get a look when the 2013 conclave opens Tuesday afternoon.

[Follow John Allen on Twitter: @JohnLAllenJr]