Jaylen Brown and Jayson Tatum are the most athletic pair of forwards the Celtics have had since Paul Pierce and Antoine Walker. We should start there because there’s a lot to unpack about these two.

Maybe we should actually back up first. Calling them “forwards” isn’t really the point because those positional denominations don’t exist in Brad Stevens’ lineup hierarchy. Brown and Tatum are both wings, or swings, the latter indicating that they can guard just about everyone between ball-handling guards and seven-foot big men.

“Greyhounds” is what former Celtic great and current radio analyst Cedric Maxwell calls them. That works.

With Brown and Tatum, the Celtics take on an entirely different form than previous incarnations. They are faster, longer, and way more dynamic. Brown and Tatum’s rapid development is one of the biggest reasons why the C’s are surging in the standings, a remarkable turn of events following the season-ending injury to Gordon Hayward. It’s also incredibly fun to watch evolve night after night.

What makes Brown especially intriguing is that he can guard up or down positionally. He’s fast enough to stay with wing runners and strong enough to body larger players. Tatum may get there too, but he’s holding his own on that end of the floor and that’s impressive for a rookie.

Defensive improvement The Celtics came into play Friday night with the league’s top-rated defense. That topic has been covered well here. Brown and Tatum are an integral part of this mix, given their versatility. The Celtics haven’t been switching as much as last year, in part because there’s fewer natural mismatches on the court. Also: Al Horford remains criminally underrated.

On offense, Brown keeps doing things you didn’t know he could do, like knocking down corner threes with confidence and dunking over people in traffic off the dribble. He’s been working on a post-up game since his rookie season that can either look brilliant or off-kilter. The important thing is that Brown isn’t afraid to fail. One of these days he’s even going to get the pump-fake and drive move from the wing down without getting called for a travel.

Right now he’s giving the Celtics 16 and 6, albeit without a ton of playmaking. That, along with subpar free throw shooting, are the only noticeable dents in his game. He’s improved his shooting dramatically and his work on the defensive boards has been a plus, as has Tatum’s.

The true measure of Brown’s impact is in his on/off splits. The Celtics are more than 12 points better than opponents per 100 possessions when he’s on the court and more than four points worse when he’s on the bench.

Cleaning the glass The Celtics were one of the worst defensive rebounding teams in the league last year. They are in the top five this season. This has become a team-wide concern from Terry Rozier, who rebounds like a big man, to Horford, who is grabbing defensive boards at the highest rate of his career.

To put it another way, Brown has both the biggest positive impact on the scoreboard among the rotation regulars when he plays and the largest negative impact on their fortunes when he sits. Dude is really important.

Tatum is a more polished offensive player and he plays with an unhurried pace that belies his young age. He likes to work the middle of the floor with varying degrees of effectiveness, but he’s quick enough to get to the basket and crafty enough to finish. Little by little, you can see him begin to establish his space in their halfcourt offense.

He has the potential to be a 20-point scorer night in and night out because he can score in so many ways. For now, he and Brown are both catch-and-shoot players from behind the arc. Both players are positively deadly from the corners, especially in transition where the Celtics thrive offensively.

The best part of Tatum’s game is his ability to get to the free throw line, where he’s an 83 percent shooter. He and Brown get there almost nine times a game. That’s a little more than Isaiah Thomas got to the line last season and he was the only Celtic who did it with any kind of regularity.

The bizarro bigs The C’s offense ranks about league average, but they are 10th in free throw rate and offensive rebounding percentage. Both areas are notably improved from last year’s team. Give credit to Aron Baynes and Daniel Theis for bumping that last number. What an effectively weird center combo those two have become.

Like Brown, we have no idea how good Tatum is going to be once he gets himself established. Even at 14 points a game, he hasn’t really taken on a huge role in the offense yet. What’s apparent is that he’s not overwhelmed by the moment or his assignments. The old heads who hang around around the Garden are universal in their belief that he’s a player.

Brown and Tatum’s development, and how quickly it happens, will in large part decide this Celtics season. When Hayward went down, the word around the team was that we’d get an extended look at the young duo. Both would have had roles even with Hayward in the lineup, but there’s no doubt his absence has accelerated their learning curve, and increased their importance.

If this is real, then the Celtics are in far better shape than we all expected, both now and into the future. At the very least, they are far more interesting than we imagined.