Conventional wisdom holds that drug addicts can't be depended upon to perform their jobs.

You certainly wouldn't want them handling hot rivets on construction sites, operating locomotives, driving buses or performing tableside with sharp knives for the customers at Benihana's. 

And when it comes to acting, you would think a drug addict just wouldn't be able to function at all, what with all the memorization the job requires, the concentration it takes to stay in character, the early arrival times on the set and then the long hours until quitting time. 

That's what's so confounding about Robert Downey Jr. This guy seems like the world's biggest screw-up, and yet he's been turning in some of the most winning performances seen on TV all season (and I'm not talking about his televised appearances in various real-life courtrooms). 

Tonight marks the last of 10 episodes of Ally McBeal in which Downey has played lawyer Larry Paul, Ally's new boyfriend. 

On the show, Downey is charming, intelligent, articulate and independent — in short, the kind of dashing, yet down-to-earth handsome prince whom Ally and her fans have hoped she would find eventually. 

Not only does he love Ally very much, but Larry is also a concerned divorced father, who tonight faces a serious decision over whether to move from Boston back to Detroit to help raise his small son, who lives in that city with Larry's ex-wife. 

The real Robert Downey Jr., 35 and married for nearly nine years, is being sued for divorce by his wife, who is reportedly pressing for custody of their seven-year-old son. In addition, with the actor out on bail following yet another drug arrest, his visitation rights may be greatly curtailed, if not eliminated. Like Larry Paul, Downey is said to love his son deeply. 

Downey is awaiting a decision on his fate following that last arrest, which happened over Thanksgiving weekend when cops entered his room in a Palm Springs hotel and found him allegedly in possession of cocaine and Valium. In court Jan. 29, a judge ordered prosecutors and defense attorneys to agree on a plea bargain by Feb. 21. 

On Jan. 23, Downey won a Golden Globe for his work on Ally. And last week, he was back on the set filming at least one additional episode to be aired later this season, which means we haven't seen the last of Larry Paul. 

Until his return, you have tonight's episode, which is as sweet an hour of television as you'll ever see, and Downey is one of the reasons why. 

He's a charismatic actor with special gifts, but he's also a drug addict. 

There are those who feel that the only way to cure people like him is to throw them in jail for as long as it takes for the craving to fade away. 

Downey's tried that cure and it hasn't worked. 

On the set of Ally, though, he seems to have found some sort of equilibrium and his work shows it. 

I hope he can resist the drugs. I hope he's had his last arrest. I hope he can stay out of court. 

But if he ever again finds himself standing before a judge, I hope the judge sentences him to go to work — on Ally McBeal or any other TV show that will take him — just as long as he doesn't intend to operate any forklifts or perform surgery.