As a general rule, professional basketball players don’t get better with age. Most career arcs in the NBA go something like this: Rookies survive on talent (and hopefully) maturity. Good players take the extra step by expanding their shooting range or developing a go-to move. Smart players understand what they can do — and more importantly, what they can’t — and after four years or so they begin to approach a peak level of performance.

If a player is very good, he will sustain that peak for four or five more years. If he is truly great, he will last longer. As Celtics coach Doc Rivers likes to point out, the number one attribute of a great player is availability.

The hard reality in the NBA is that for the vast majority of players once they identify something they do particularly well — be it shooting corner 3’s, rebounding or defense — that becomes their means for staying employed. Bruce Bowen never worked on his dribble-drive game because A) he didn’t need one and B) the Spurs would have had no use for him if he had tried. To put it another way, at a certain point most NBA players stop evolving.

Paul Pierce is not like most NBA players. On Monday, he was named Eastern Conference Player of the Week after he averaged 22 points, eight rebounds and led the Celtics to four straight wins. It was a nice acknowledgment of the work Pierce did as he helped guide the Celtics through the early phase of their post-trades transition.

It also seemed like a reasonable time to raise a larger point: Pierce has been the Celtics' best player this season, culminating a four-year process that has seen him transform from a high-volume scorer into a model of offensive efficiency.

To get there, we should start at the beginning when Pierce made his mark as an elite-level scorer, one of the absolute best of the first half of the decade. There are many informed observers around this region who consider him the best all-around offensive player to ever suit up for the franchise.

His career peaked in 2006 when he put up almost 27 points, seven rebounds and five assists per game. Unfortunately for Pierce, that team won 33 games and his teammates included Ricky Davis, Mark Blount and the immortal Raef LaFrentz. The two things are related.

In Pierce’s own words, he was the classic example of a great player on a bad team, and while that remark offended the delicate sensibilities of the self-appointed guardians of what athletes can and can not say, he was absolutely correct. 

For a while it also looked like that comment was going to serve as Pierce’s epitaph for his time in Boston: Great player. Bad teams. Thanks for the memories with Antoine. Have fun in Portland. 

But Pierce was granted the rare chance to write another chapter in his legacy when the Celtics not only resisted the urge to trade their top asset, but also surrounded him with Kevin Garnett and Ray Allen. Over the next four seasons Pierce’s numbers dropped in scoring, rebounding and assists, which was exactly the point. If they hadn’t, the Celtics wouldn’t have worked.

The trade-off was that Pierce was granted a new level of appreciation for his commitment to defense, as well as his willingness to have the ball in his hands and make decisions at the end of games. His numbers have also been remarkably consistent during this stretch, but something deeper has been happening this season.

Pierce is shooting over 50 percent from the floor for the first time in his career. He’s also posting his best free throw percentage, committing fewer turnovers and his defensive rebounding is back to where it was before Garnett arrived. We can go further still into the wonkier realm of advanced stats. According to the +/- numbers on Basketball Value, the Celtics are 19 points better when Pierce is on the court than when he is not. No player in the league has a bigger impact on his team.

Pierce’s statistical improvements have been subtle — and owe more to good health than any newfound skill — but they have been very real. They’ve also only been a part of a larger story. 

When the Celtics needed someone to run the team while Rajon Rondo was hurt, he did it. When they need someone to guard the star forwards in this league, he does it while sacrificing at the offensive end. Pierce — because he is Pierce — believes with all his heart that if he absolutely had to go out and drop 25 a night he could still do it, and there are games when he does. Going back to Rivers’ maxim on availability, Pierce has also played every game, which is no small accomplishment on this team. 

It’s a fun diversion to try to determine which of the Celtics’ four All-Stars is the most indispensible. They have never won a title without a healthy Garnett, who is by far their best defensive player and always has been. Rondo is the undisputed brain on the court and the creative genius of an otherwise vanilla operation. Allen is the engine that runs their halfcourt sets and the floor-spacing shooter that is so crucial to everyone else’s game.

For whatever reason Pierce is often left out of the conversation. His excellent play has been so ingrained in our consciousness, it’s almost as if he is taken for granted like No. 9 Park or the view of the city from the Mass Ave. Bridge.

Is he the one player the Celtics absolutely must have healthy in order to win a championship? That’s probably still Garnett, but has Pierce been the Celtics’ most valuable player this season? He’s been the most durable, the most versatile and by many objective measures, he’s also been their best player.

Pierce is not playing the best basketball of his life, but these are the best days of his career and it’s been quite a second act.