FOXBOROUGH -- At first glance, it would appear that change is in the air at Gillette Stadium.

After playing a 3-4 base defense the last few seasons, the Patriots showed a lot of 4-3 in their preseason opener last Thursday against the Eagles, and were able to get good pressure on a banged-up Philadelphia offensive line, coming away with a pair of sacks in the first half when the starters were in the game.

With an impressive collection of defensive linemen -- Richard Seymour, Vince Wilfork, Jarvis Green and Ty Warren (who sat out the preseason opener), as well as rookies Myron Pryor and Ron Brace -- and a lack of depth at linebacker, the move certainly makes sense from a practical standpoint, and could herald an overall shift in New England’s defensive philosophy.

When asked this week, coaches and players kept their cards close to the vest, saying they are equally as comfortable in the 3-4 as they are in the 4-3, and could change looks at the drop of a hat. If so, the Patriots will follow the model put forth by teams like Baltimore in that they’ll go from week-to-week, giving different teams myriad looks in an attempt to keep the rest of the NFL guessing when it comes to game-planning for the New England defense.

“We have the versatility to play in a lot of different fronts, a lot of different packages, whatever is gonna give our team the edge,” Seymour said. “Whether it’s a 3-4 or a 4-3, whatever is going to give us the best chance to win -- that’s what we’re going to do.”

But how much will things really change for the Patriots’ defense if they do shake up the look of the front seven? An examination of how New England operated out of the 4-3 against Philadelphia reveals that while most of the front seven will have the same gap responsibilities in the 4-3 that they had in the 3-4, it won’t look much like a traditional 4-3.

“We had three or four different 4-3 alignments,” Patriots coach Bill Belichick said late last week when asked about the defense against the Eagles. “Sometimes we were to the tight ends and sometimes we were away from the tight end on the strength.

“We mixed in a little over, a little under and some nickel-type fronts.”

As Belichick stated, New England played some 4-3 over, which shifted the four defensive linemen to the strong side of the Philadelphia defense (the side with the tight end). In the 4-3 under, which was also featured by the Patriots, the four down linemen shifted to the weak side of the defense, away from the tight end. The biggest wrinkle came in the use of defensive ends Derrick Burgess and Tully Banta-Cain, each of whom lined up wide of the offensive tackle like an outside linebacker, but still started with his hand on the ground like a defensive end.

While the 4-3 could present more opportunities for New England’s defensive ends to rush the passer -- traditionally, defensive ends in four-man fronts can get sacks by the bushel -- Seymour said Thursday that it’s not always about bringing down the quarterback.

“Sacks can be overrated. It’s about getting pressure on the passer and taking care of your responsibilities first,” he said. “[There’s] a time and a place for everything, and if it calls for us to penetrate and get in the backfield, then that’s what we’ll do.”

According to Seymour, the overall responsibilities for the defensive linemen in the 4-3 will be the same as they were in the 3-4. Traditionally, the Patriots’ 3-4 defense has been a two-gap system, meaning that each defensive lineman has been responsible for two gaps on each side of him, with the idea being you have two linemen responsible for every gap.

The 4-3 is traditionally more of a one-gap defense, but that doesn’t mean New England won’t put its own spin on things.

“Sometimes, we’ll two-gap on that same 4-3 front as well,” Seymour said. “Some teams have different philosophies where it’s a one-gap defense, but we’re still two-gap, and everybody has responsibilities for two gaps.”

For the linebackers, things wouldn’t really change that dramatically, with the biggest change coming with fewer pass-rushing opportunities for the outside linebackers. And more is on the shoulders of the middle linebacker when it comes to making the calls and directing traffic within the defense.

“It doesn’t really change that much. I played ‘will,’ the inside in the 3-4,” said Jerod Mayo, who played at the inside linebacker spot in New England’s 3-4 defense last year, but was at the middle linebacker spot last Thursday in the 4-3. “It’s a little bit easier. I don’t have to wrestle with those linemen as much.”

“In a 3-4, he’s on the weak side. In a 4-3, he could be in the middle, on the weak side, on the strong side,” Belichick said of Mayo’s movement. “[But] from a technique standpoint, those responsibilities stay the same. There’s a lot of carryover.”

Mayo sounds like he prefers operating out of the 4-3 -- “I can think a lot faster and get to the ball,” he said. But it’s not like the middle linebacker in the Patriots’ 4-3 has free reign to roam -- he still has to stay disciplined within the overall context of the defense.

“Not really,” he said when asked about having a little more freedom to freelance in the 4-3. “Not in our 4-3 -- it’s a little different.”

In the end, the players may be shuffled around the field like chess pieces, but the overall approach remains the same.

“All of our players in the front seven play with the same techniques, regardless of what the front is. We still fundamentally do the same thing,” Belichick said. “There are some adjustments when players play different alignments. But the fundamentals of those positions, basically, we try to keep those the same so we’re not changing the techniques.”