Boston ? John Edwards cannot donate the optimism, which seems to run deep in his marrow, to John Kerry. He cannot graft his electric smile or transfer his energy onto the top of the ticket.

But he can argue the case.

That’s the gift of the trial lawyer in Edwards: taking a set of facts, molding them, then persuading someone else to believe them.

Now Edwards’ client is Kerry.

He has been making the case for the Massachusetts senator for months. But Wednesday night, the audience of voters expanded exponentially. And Edwards deftly employed the same style that made him so appealing throughout the primaries, repeatedly bringing cheering Democrats in the convention hall to their feet.

If there was a word that stood out it was a simple one, the second-person singular, “you.” He used it repeatedly to build a direct connection with his listeners, to draw them closer, to try to seal the verdict.

He used it nine times in one paragraph alone:

“And you know what I’m saying,” Edwards told them. “You don’t need me to explain it to you, you know — you can’t save any money, can you? Takes every dime you make just to pay your bills, and you know what happens if something goes wrong — a child gets sick, somebody gets laid off, or there’s a financial problem, you go right off the cliff.”

Edwards, a first-term senator from North Carolina, has a way of taking all the obvious touchstones of “better tomorrows” and crafting them to sound less like a speech and more like a conversation.

“We hear a lot of talk about values,” Edwards said. “Where I come from, you don’t judge someone’s values based on how they use that word in a political ad. You judge their values based upon what they’ve spent their life doing.”

He uses his life story as allegory to tell the story of overcoming hardships. Some, he talks about often, such as his humble beginnings and the shabby treatment of his mill-worker father, giving voice to the workers who “had lint in their hair and grease on their faces.” Others, he never talks about, like the death of his first-born son, Wade, at age 16.

Sen. John Edwards of North Carolina gestures after speaking to delegates during the Democratic National Convention at the FleetCenter in Boston. Audience for the first-term senator was enthusiastic Wednesday, reinforcing Sen. John Kerry's choice to put Edwards on the Democratic presidential ticket.

And once again, somehow, he managed to do it without sounding saccharine.

He also did not make the mistake of talking more about himself than he did John Kerry.

“He strengthens Kerry. That’s what a vice presidential candidate does. He’s supplemental,” said Walter Mondale, a former vice president who should know, in an interview on the convention floor:

Indeed, he does supplement Kerry in fundamental ways. He can tell the story of the working class and reach out to black voters in ways that Kerry cannot.

Democratic delegates on the convention floor shared a common catalog of adjectives to describe him. “John Edwards brings a new idea and a new thought process to the ticket,” said Les Miller, a delegate from Tampa, Fla. “He’s energetic. He’s vibrant. He’s got young kids. … What optimism does (Vice President) Cheney bring? This man is young, with new ideas.”

Republicans have a ready list of complaints. That Edwards is too young, too green, too shallow.

On this night, that wasn’t the view in the partisan hall. “I think he has soul,” said Pat Ackley, a delegate from Oregon. “He can parse sentences to the very essence. When he’s talking about jobs, he’s not using big words about economics. He talks about jobs. He’s able to cut through the political mumbo jumbo.”

But Ackley is not among those who think that Kerry needs Edwards to fill in any personality gaps. “He could be a wonderful president without Edwards.”

Nonetheless, one pressing question remains: How much does client Kerry need Edwards as his advocate? What if Edwards makes Kerry’s case better than Kerry himself? A good trial lawyer doesn’t care.

As long as he wins.