As the Eagles head toward the offseason, trying to figure out what went wrong with them and what is still right with them, there is no equation more difficult to solve than the defense.

Forget about judging only the players. Deciphering the true nature of the defense means sorting through the styles and peculiarities of two defensive coordinators and two defensive line coaches.

On Thursday night against the Bengals, for most of the game the defense was very good against a respected offense. It wasn't just very good. It was nasty, in the old-fashioned Eagles way.

Who gets the credit for what is going well now, and who gets the blame for what went badly then? And is it just another late-season run of fool's gold? Good questions, and ones that won't be fully answered by the end of the season Dec. 30. The improvement, however, is unmistakable.

The Eagles played six games with Juan Castillo as coordinator and Jim Washburn as line coach (3-3), then six games with Todd Bowles as coordinator and Washburn (0-6), and now two games with Bowles and Tommy Brasher (1-1).

If you want to play amateur psychologist, with a knowledge of some of the personalities involved, you would guess that Castillo tried to make things work despite the autocratic presence of Washburn and his affinity for the gimmicky wide-nine alignment of the front four. You also would guess that Bowles wasn't as yielding and there was division during that long losing streak. And, based on much better play against Tampa Bay and Cincinnati, veteran line coach Brasher came in and simplified everyone's life.

Instead of setting the tone for the defense by being a freelancing island apart from the others, the defensive line has narrowed its stance, helped close the gaps in the running game, and still been able to put pressure on the quarterback.

Through the first three quarters last night, the defense tried to keep the Eagles in the game while the offense was intent on giving it away with turnovers. The defense recorded six sacks of Andy Dalton for the night and did a good job of limiting running back BenJarvus Green-Ellis. Going in, the Eagles hadn't gotten more than three sacks in a game and had just 22 for the season.

With Dalton getting pressured, suddenly the pass coverage was a lot better and the linebackers could be more aggressive throwing themselves into the run gaps. (A cynic would point out that the pass coverage also has been a lot better the last two games with Colt Anderson replacing Kurt Coleman at the free-safety position.) Whatever the individual reasons, the defense played as a team.

As with almost everything else this season, the effort was largely wasted. On this night, it was wasted because the Eagles had four turnovers and a punt blocked, and mostly couldn't get out of their own way without making a crippling mistake.

When the Eagles held a 13-10 lead early in the second half and then pinned Cincinnati back to its own 15-yard line with a punt, the defense responded to the moment with a two-sack series that got the offense the ball back at the Eagles' 47-yard line.

Instead of taking the team down the field to expand the lead and really grab the momentum of the second half, Nick Foles threw a bad interception and the defense was on the spot - and on the field for most of the next 10 minutes of play as one turnover followed another.

As bad as it got - and the 34-13 score is plenty bad enough - it could have been worse. The defense held the Bengals to a field goal after a Clay Harbor fumble set up Cincinnati in the red zone. It held again on another short-field drive until some genius on the field-goal coverage unit yelled out what referee Carl Cheffers said were "disconcerting signals." Whatever those are, they are unsportsmanlike, according to Cheffers, and the Bengals got a late touchdown instead.

It wasn't a perfect night for the defense - nothing goes that well this season - but it was a night in which, until they were beaten down by the offense's mistakes, it looked like a real defense.

Mark that as a big improvement over the slop of the Bowles-Washburn era, and maybe it is even for real. That's for the organization to figure out. Just put it on the list.

Contact Bob Ford at bford@phillynews.com. Read his blog at www.philly.com/postpatterns. Follow on Twitter @bobfordsports.