Conventional NFL wisdom says that you never, ever trade a franchise quarterback—no matter the size of his contract nor the creakiness of his knees. And the object lesson in why comes courtesy of the Miami Dolphins, 1993 edition. At the time Miami’s starting quarterback was Dan Marino, who by then had already established himself as one of the game’s best passers. But when he suffered a season-ending Achilles injury, an unheralded backup from Utah named Scott Mitchell stepped in and performed masterfully, orchestrating the Miami offense seamlessly and nearly leading the team to the playoffs. When the season ended, a slew of commentators and remarkably unsentimental fans started asking whether the Dolphins might not be better off keeping the younger Mitchell and trading the now-battered Marino, who could probably fetch a clutch of star players or, at least, some high draft picks.

Dolphins Coach Don Shula thought better of it—a decision neither he nor any of those fair-weather fans ever regretted. The following season, Marino threw for more than 4,000 yards and 30 touchdowns. He went on to play six more seasons, leading Miami to the playoffs five more times while shattering every meaningful lifetime passing record. Mitchell ended up in Detroit with a plush, three-year, $11 million contract. He had one strong season, in 1995, but had played his way out of Detroit and onto another team’s bench by the time Marino retired. Mitchell’s flash of greatness in Miami turned out to be just a fluke—a function of the fact that opposing defenses hadn’t yet figured out his weaknesses, which turned out to be considerable.

Fast-forward six years, and we find the New England Patriots in almost precisely the same predicament as Miami was in 1993. Their injured star is Drew Bledsoe, one of the NFL’s best signal callers. Early in the season, a freakish hit from a Jets linebacker sent Bledsoe to the hospital—and out of the starting lineup—with severe internal bleeding. Patriots coach Bill Belichick turned the offense over to an unknown backup, second-year player Tom Brady. And Brady has worked wonders. He went four games without throwing a single interception, then guided the Patriots to upset victories over Indianapolis, New Orleans, and the dreaded New York Jets, compiling an overall record of 7-3. Now the Pats, winless at the time of Bledsoe’s injury, look like a playoff team.

Enter the quarterback controversy. Even before doctors pronounced Bledsoe fit to play two weeks ago, a new chorus of columnists and ungrateful fans were calling for Belichick to make Brady the permanent starter. Of course, doing so would probably mean letting Bledsoe go down the road—either via trade or waivers—since his contract (four years, $30 million) is too high for a second-stringer. But that’s a risk Belichick is willing to take, because a week ago he announced that Brady was his man for the rest of the year.

So, did Belichick forget about the whole Scott Mitchell debacle? Hardly. He simply understands that the NFL has changed dramatically in the last seven years. In 1994, the year after Mitchell set the league on fire, the NFL adopted a salary cap, and a player’s value became not simply a function of how he performed on the field but also how much he cost. General managers have operated on this assumption for a while, dispatching legendary but aging stars like Jerry Rice and Bruce Smith in order to free up salary cap space. But for some reason, quarterbacks have been largely exempt from this sort of calculus. Belichick obviously thinks it’s time that changed. And he’s right.

The Bledsoe-Brady controversy is a perfect example of how the introduction of a salary cap has turned NFL conventional wisdom on its head. Indeed, the irony of the situation is that all the Boston talk-radio cranks convinced that Brady is a better quarterback are almost certainly wrong. Sure, the guy has fine mechanics and uncanny poise in the pocket. But despite his torrid start, four teams with solid pass defenses—Buffalo, Denver, Miami, and St. Louis—contained him handily. Brady’s rolled up his biggest numbers against the Colts, whose pass defense would have trouble keeping some 1-AA college teams out of the end zone.

Bledsoe, on the other hand, has about as good a stat sheet as you can compile in nine years of professional play. He made the Pro Bowl in his third year and led the Patriots all the way to the Super Bowl in his fourth. In 1995, he became the youngest player ever to throw for 10,000 yards; his current career stats include 136 touchdowns and nearly 30,000 yards. And he’s done all this despite an ever-changing roster of coaches that would make George Steinbrenner blush. Belichick is Bledsoe’s third head coach; the Pats’ current offensive coordinator, Charlie Weis, is his fourth.

So if this were simply about which quarterback has more talent, you’d be a fool to choose Brady. But think about what Bledsoe could fetch if the Patriots, a team with gaping holes all over the place, traded him. In April, the Atlanta Falcons gave up a first-round draft pick and a solid wide receiver-kick returner for Michael Vick. Bledsoe would probably claim an even higher bounty: Paul Zimmerman, Sports Illustrated football Svengali, recently suggested Bledsoe would probably fetch a starter plus two first-round draft picks.

Jettisoning Bledsoe would also take his $7.5 million per year contract off the books—Brady makes only $300,000 per year—next season or the season afterward, freeing up money for a desperately needed offensive lineman or two, plus a playmaker at wide receiver. (Because of the complicated rules of the cap, the Patriots could get rid of Bledsoe next year or the year after without taking a debilitating hit, though it depends in part on how they get rid of him.) In other words, you’re trading proven greatness at quarterback for four or five starters. Even if Brady turns out to be mediocre, all the extra quality players make the transaction a net winner for the team, and the surest way to turn this year’s squad—which is performing far beyond its talents, thanks to good coaching and a bit of luck—into a serious Super Bowl contender.

If Bledsoe really wants to stay with the Patriots—and, to his credit, he’s been the epitome of a loyal, club-friendly athlete for his entire stay in Foxboro—he’s welcome to take a pay cut. Otherwise, he should go. Harsh? Perhaps. But that’s the new reality of the NFL. Someday, the Tom Brady decision will turn out to be an object lesson too.