The psycho babblers call it "inductive reasoning." I consider it a chance to write about ducks on a football blog. We'll call it the Duck Test, and here goes: If it looks like a duck, swims like a duck and quacks like a duck, then it probably is a duck.

Are the Minnesota Vikings the duck in our little analogy here? They have the record (4-1) of playoff contenders. They have a quarterback who has played with top-10 efficiency, thanks to some help from a receiver who is a legitimate MVP candidate. Their defense is tough against the run and hasn't been burned by the pass. Their special teams have directly impacted two victories and their schedule suggests the real possibility of seven victories by their Week 11 bye.

Our job is to determine at what point to apply the Duck Test. The Vikings are tied for the NFL's second-best record after five weeks. Are we ready to call them legitimate playoff contenders? Or do we need to see more from a team universally projected to finish last in the NFC North this season?

It's not an easy question to answer, and I'm not sure we'll get there in this post. Some of the team's most established veterans are pleasantly surprised by this start, after all, and everyone recognizes the perils of invoking deep truths in the second week of October.

"Looking at it in the offseason," defensive end Jared Allen said, "I couldn't have told you we were going to do this. I thought it was really going to be a year where each game was going to mean something. There were no expectations. I had no expectations. I mean, you always say you want to win the division and all that, but ... "

Indeed, preseason pessimism was based mostly on how many key positions were manned by unproven personnel. Entering the season, coach Leslie Frazier's career record was 6-16. Offensive coordinator Bill Musgrave had never been in charge of an NFL offense that ranked higher than No. 19 in points scored. Defensively, Alan Williams had just been hired for his first coordinator job.

Quarterback Christian Ponder had 10 career starts, and the Vikings were using rookies or first-time starters at seven positions: left tackle (Matt Kalil), right guard (Brandon Fusco), tight end (Kyle Rudolph), nose tackle (Letroy Guion), middle linebacker (Jasper Brinkley), free safety (Harrison Smith) and place-kicker (Blair Walsh).

Frazier, however, suggested that a full offseason of chemistry-building and scheme implementation smoothed over many of those rough edges. "I feel like we're about where we should be," he said.

Added Ponder: "We knew we had a good team going into this thing. I know everyone else is surprised that we're 4-1. What stinks is we should be 5-0. We had that close game against Indianapolis [a 23-20 loss in Week 2]. We've always had a good team."

Or, more precisely, the potential to be one. The big question is whether the Vikings are on a sustainable path. Is it possible for Ponder to continue completing 69 percent of his passes, while throwing an average of one interception per 79 attempts? Can Percy Harvin maintain his NFL-best average of 8.4 yards gained after each catch, via Pro Football Focus?

Do we think the run defense will keep limiting opponents to 3.2 yards per carry, tied for the second-best mark in the NFL? Can the pass defense knock away passes at its current rate of more than nine per game? And is Walsh good for 12 out of every 13 field goal attempts, along with an average of more than three touchbacks on kickoffs per game?

What you just read is a two-paragraph summation of why the Vikings are 4-1. And it fits neatly into what Frazier recently espoused as a sustainable vision for winning.

"I believe being able to play good defense, being able to stop the run and not give up big plays in the passing game, gives you a chance at being successful every week," he said. "If your special teams can do a great job in that area as well, where you can win that special-teams battle, along with being able to run the football, and not turn the ball over, and when you get people playing eight- or nine-man fronts, being able to have a quarterback who can execute in those situations, I think that's a winning formula. I've seen it as a player and I've always believed it as a coach as well.

"I know there are some teams who buck that a little bit by putting up a lot of points and a lot of yards. But I just think in the long term, to be good in our league for a long period, and that's what we're hoping to be able to do, not just a one-year wonder or two- or three-game wonder; we want to be a football team that's going to be good for a long period of time. You need to be able to play good defense and we're doing that right now. The results are, we're on the upside from a win-loss standpoint."

Based on those standards, my sense is the Vikings' offense is positioned for continued efficiency with Ponder, Harvin and tailback Adrian Peterson. It is fair, however, to question whether it can play effectively from behind.

There is no reason to think the Vikings can't sustain their run defense, long a hallmark of Frazier's defenses when he was the Vikings' coordinator. But will teams eventually find holes in their pass defense? That's a reasonable possibility when you realize there are two rookies -- Smith and cornerback Josh Robinson -- among their top-five players.

The most encouraging development for the Vikings is that they are playing better than they did at the start of the season, which began with a shaky overtime victory over the Jacksonville Jaguars and the loss to the Colts. Sunday's 30-7 victory over the Tennessee Titans was probably their most complete victory in three seasons.

That's when they first looked to me like ducks. Eventually, it won't matter how they're managing to look, swim and quack like them. Their record will say they're a duck and that's what they'll be. That point could be coming soon. I'm not ready to say they will make the playoffs, but we have at least seen evidence of how they could.