It’s late in the first quarter. A play ends, and seconds later Tom Brady has his team back at the line. He gives a hand signal to his receiver, a tap to his offensive linemen. “Alabama! Alabama!” The ball is snapped. An outlet pass goes to Stevan Ridley, who rumbles to the Houston 40-yard line, another first down. Subs run in. Soon, the Patriots are back at the line. Except now, running back Shane Vereen is lined up out wide. The Texans are scrambling. Brady takes the snap and hits Vereen on a quick hitch. Vereen dips around linebacker Bradie James and then spins back inside, gaining 25 yards before he’s done.

The next play is the same play, with the same personnel, with zero time for the defense to recover. The three receivers to Brady’s left crisscross around defenders while Aaron Hernandez, who was lined up as a back to Brady’s left, dashes to the flat. He makes the catch and takes it to Houston’s 1-yard line. The same 11 Patriots sprint to the line, but Vereen is now in the backfield. The play is a run to the left, and he’s into the end zone untouched. Touchdown, New England.

Since Tom Brady became the starting quarterback in New England 12 years ago, the Patriots have finished in the top 10 in scoring 11 times, but the way they’ve gotten there hasn’t been nearly as consistent. In Brady’s early years, Bill Belichick built his offense not around his quarterback, but rather to support him, with a steady supply of dependable receivers and a physical running game. It was when Brady moved from trusted game manager to outright star that he became the offense’s centerpiece, and the need for reliable bolstering was replaced with the pursuit of a cast that could push him even further.

First it was with Wes Welker, Randy Moss, and a pass-happy shotgun spread offense. More recently, with Rob Gronkowski and Aaron Hernandez, the offense became a two–tight end–based attack. With Gronkowski set to miss the rest of the playoffs, and Ridley and Vereen continuing to improve, the Patriots appear to be evolving again, this time relying on two running backs. Throw in three different offensive coordinators — Charlie Weis, Josh McDaniels, and Bill O’Brien — and it seems that the only constant in New England, other than Belichick and Brady, has been change.

But what’s allowed New England to maintain its success among the shifts is that its quarterback and coach aren’t the only things that have remained the same. The core of the Patriots’ offensive system has been threaded through its various stages, both stabilizing the transitions and allowing the next evolution. The design and organization of New England’s system is better suited than any other to adapt to an NFL game in which change — of personnel, of trends, of schemes — is the only certainty.

To an almost shocking extent, NFL offenses are homogeneous. Given that every NFL team is in, roughly speaking, the same circumstances in terms of money, resources, practice time, and facilities, this homogeneity makes some sense. After all, “football’s always football,” as newly minted San Diego Chargers head coach Mike McCoy recently said. “Everyone’s running the same plays, and it’s a matter of some running one concept more than another team is. It all boils down to the same thing.”

There are essentially three main offensive “systems” in the NFL: West Coast, Coryell, and Erhardt-Perkins. Given that every NFL team runs basically the same plays, each of these NFL offensive families is differentiated mostly by how those plays are communicated.

To oversimplify, the West Coast offense, made famous by Bill Walsh and still the most popular system in the NFL, uses what is essentially a memory system. On running plays, the same two-digit numbering system as most NFL and college teams is used. Passing plays, however, are typically denoted by the primary receiver’s route, such as Z-In, X-Hook, while the rest of the players are required to memorize their tasks. This system is as old as football itself, which is no surprise given that Walsh’s onetime mentor Paul Brown is credited as much as anyone with inventing the modern conception of huddles, game plans, and play calls. For more than 20 years, this system has been the dominant one in the NFL.

The Coryell system, named after former San Diego Chargers head coach Don Coryell and used by coaches such as Norv Turner, Ernie Zampese, and Mike Martz, is built around the concept of a route tree. Many teams use a route tree (which is the idea that the base route is straight up the field, and the other routes consist of break points off that original path), but the Coryell system uses the tree as the foundation of its play-calling system. For example, the Troy Aikman–era Dallas Cowboys frequently called a play called “896,” which told one outside receiver to run a square-in route (“6”), the tight end to run a seam straight up the field (“9”), and the split end to run a skinny post (“8”). The idea was that, using the route tree, a coach could effectively call any pass combination and all a receiver had to know was the number associated with his route.

In recent years, as offenses and defenses have grown more complex, these systems have started crumbling under their own weight. With multiple formations and personnel groupings, calls that began as “22 Z-In” have gotten unwieldy.

In the Coryell system, the elegance of the three-digit route-tree system has been rendered almost entirely obsolete. Because NFL teams operate predominantly in one-back formations, there are often more than three players running routes, and calling any pass play means having to use both numbers and words (“896 H-Shallow F-Curl”). More critically, the numerical route-tree system gives coaches and players flexibility where they don’t need it and not enough where they do. The “benefit” of a route-tree system is the ability to call any passing concept a coach could dream up, but that option is of very little use. Assuming the route tree has 10 routes (0-9), a three-digit tree gives an offense 59,049 different possible route combinations. That’s absurd. And yet, the route tree by definition only has 10 possible routes, much fewer than any NFL team actually runs. This means that any other route must be called by name, thus defeating the very purpose of having a route tree.

This effectively makes the Coryell system sound a lot like current West Coast offense play calls, which have no organizing principle and have morphed into monstrosities like “Scatter-Two Bunch-Right-Zip-Fire 2 Jet Texas Right-F Flat X-Q.” The advantage of a play call like this is that it informs a player of his job better than other systems do. The disadvantage is that it’s excessively clunky, and plays that are conceptually the same can have wildly different calls.

New England’s offense is a member of the NFL’s third offensive family, the Erhardt-Perkins system. The offense was named after the two men, Ron Erhardt and Ray Perkins, who developed it while working for the Patriots under head coach Chuck Fairbanks in the 1970s. According to Perkins, it was assembled in the same way most such systems are developed. “I don’t look at it as us inventing it,” he explained. “I look at it as a bunch of coaches sitting in rooms late at night organizing and getting things together to help players be successful.”

The backbone of the Erhardt-Perkins system is that plays — pass plays in particular — are not organized by a route tree or by calling a single receiver’s route, but by what coaches refer to as “concepts.” Each play has a name, and that name conjures up an image for both the quarterback and the other players on offense. And, most importantly, the concept can be called from almost any formation or set. Who does what changes, but the theory and tactics driving the play do not. “In essence, you’re running the same play,” said Perkins. “You’re just giving them some window-dressing to make it look different.”

The biggest advantage of the concept-based system is that it operates from the perspective of the most critical player on offense: the quarterback. In other systems, even if the underlying principles are the exact same, the play and its name might be very different. Rather than juggling all this information in real time, an Erhardt-Perkins quarterback only has to read a given arrangement of receivers. “You can cut down on the plays and get different looks from your formations and who’s in them. It’s easier for the players to learn. It’s easier for the quarterback to learn,” former Patriots offensive coordinator Charlie Weis said back in 2000. “You get different looks without changing his reads. You don’t need an open-ended number of plays.”

This simplicity is one of the reasons coaches around the league have been gravitating to the Erhardt-Perkins approach. “Concepts benefit you because you can plug different guys into different formations, into different personnel groups, and if they understand the concept, it gives you more flexibility,” Atlanta Falcons offensive coordinator Dirk Koetter recently explained. “The number system restricts you because it doesn’t allow you to cover all the combinations you want to use, so you have to get into so many tags that eventually you’re calling everybody’s route. In route concepts, one word can describe anything. In my experience, most kids can visualize one-word concepts better.”

There have been some noted successes of the Erhardt-Perkins approach — famously with the New York Giants under Bill Parcells — but it’s had some failures, too, particularly the plight of Rich Kotite’s Jets while Erhardt served as offensive coordinator. Ray Perkins, who hired Parcells while head coach of the Giants and was later head coach of the University of Alabama and Tampa Bay Buccaneers, is at Jones County Junior College in Ellisville, Mississippi. The ideas underlying the system are sound, but it’s the Patriots who have made it their own.

For many years, the Erhardt-Perkins offense was known as the original ground-and-pound, a conservative, run-first offense summed up by Erhardt’s mantra, “You throw to score and run to win.”

With the help of his assistants, Belichick’s primary innovation was to go from an Erhardt-Perkins offense to an Erhardt-Perkins system, built on its method of organizing and naming plays. The offense itself would be philosophically neutral. This is how, using the terminology and framework of what was once thought to be the league’s least progressive offensive system, Brady and Belichick built one of the most consistently dynamic and explosive offenses in NFL history. From conservative to spread to blistering no-huddle, the tactics — and players — have changed while the underlying approach has not.

Let’s look at a play that has long been a staple of the Patriots attack. This is actually two different concepts put together — “ghost/tosser,” which has the Patriots run the ghost concept to one side and the tosser concept to the other. Ghost has the outermost receiver, whoever it is, run a vertical route, one inside receiver run to a depth of roughly eight yards before breaking flat to the outside, and the innermost receiver run immediately to the flat. It’s a form of the “stick” or “turn” concept that essentially every NFL team uses. On the other side, tosser means that the receivers run the double-slant concept. The page below is from the Patriots’ playbook.

The theory here is that no matter the formation, there is an outside receiver, an inside receiver, and a middle receiver, and each will be responsible for running his designated route. For the quarterback, this means the play can be run repeatedly, from different formations and with different personnel, all while his read stays effectively the same. Once receivers understand each concept, they only have to know at which position they’re lined up. The personnel and formation might cause the defense to respond differently, but for New England those changes only affect which side Brady prefers or which receiver he expects to be open. This conceptual approach is how the Patriots are able to run the same basic plays, whether spreading the field with four or five receivers or using multiple tight ends and running backs.

The most recent innovation to fall into New England’s Erhardt-Perkins framework is a commitment to the no-huddle. In 2012, the Patriots were the league leaders in total plays, first downs, points, and yards — all by a significant margin. Other teams have dabbled in the no-huddle, but they can’t commit to it like the Patriots can, for one simple reason: terminology. No team that uses the Coryell or true West Coast systems can adapt easily to a fully functional up-tempo no-huddle because, simply, they can’t communicate that efficiently. The Patriots are built to communicate in one- or two-word designations, and so, with judicious use of code words, it’s simply a matter of translating what they already do into a no-huddle pace.

This marriage of terminology and technique, of efficiency and elegance, is what makes the Patriots so mesmerizing. Like NFL offenses, in recent years NFL defenses have also become too wordy, relying on long-winded calls designating scheme and technique and impractical checks. With the speed at which New England operates, the message for defenses has become clear: fix your terminology or perish. For opposing offenses, the mandate is less direct but just as imperative. The Patriots have set the standard for modern offense, and if teams are going to keep up, they’ll need to change not how they play, but how they talk.