There is a passage in Master and Commander, the first of Patrick O'Brian’s acclaimed series of historical sea novels, in which Stephen Maturin casually refers to the wealth of James Dillon, one of his shipmates.

“Surely to God you would never call me rich?” Dillon asks with some asperity.

Maturin: “I have ridden over your land.”

Dillon: “It’s three-quarters of it mountain, and one quarter bog; and even if they were to pay their rent for the rest it would only be a few hundred a year – barely a thousand.”

Maturin: “My heart bleeds for you. I have never yet known a man admit that he was either rich or asleep: perhaps the poor man and the wakeful man have some great moral advantage.”

I was struck by that colloquy when I first read it, and it seemed even more apt when I came across it again last weekend, on a day when much was being made of the revelations in the tax returns released by Republican Senator Scott Brown and his Democratic challenger, Elizabeth Warren. Neither candidate grew up wealthy, but their tax returns confirm what everyone already knows: Both have risen high and done very well. Yet rather than make the most of their success – and the intelligence, talent, and merit it implies – both preferred to play up the modesty of their past.

“People have read my book. They understand where I’ve been,” said Brown, whose memoir details a Dickensian background of hunger, violence, and sexual abuse. Warren stressed that she is “the daughter of a maintenance man who has lived the American dream.” Each candidate, meanwhile, was at pains to emphasize the other’s wealth. Brown’s campaign manager sniped at “Millionaire Warren” for being so “firmly entrenched in the same ‘1 percent’ she rails against,” while Democrats issued a press release lambasting Scott Brown as “a millionaire pretending to be an ‘everyman’ while attacking Elizabeth Warren for her success.”

I don’t know why candidates should gain some moral advantage from pointing to their own humble roots while deriding their opponent’s current prosperity. It’s one of the oldest storylines in American politics, however, and it would be futile to expect Warren and Brown to pass it up – particularly when Brown’s regular-guy-who-drives-a-pickup shtick was so successful in 2010.

Of course, true moral standing isn’t achieved through accidents of birth or campaign image-crafting. It must be earned. And judging by their tax returns, neither Brown nor Warren seized a readily available opportunity to demonstrate the moral integrity that comes from shaping their deeds to their words.

For Warren, who demands higher taxes on the wealthy and blasts the tax code for “giving tax breaks to the already-rich,” voluntarily paying a slightly higher income tax rate on her Massachusetts return should have been a no-brainer. Since 2002, the Bay State has given taxpayers the option of paying 5.85 percent, rather than the usual 5.3 percent – a perfect opportunity for an affluent progressive like Warren, who is passionate about the “social contract” that obliges the rich to “pay forward” more of their wealth in taxes, to live up to the values she espouses.

Instead she kept the money for herself. “I paid my taxes,” Warren says, “and I did not make a charitable contribution to the state.” That was her right. But shouldn’t someone so vocal on the subject of tax fairness choose to lead by example instead?

And shouldn’t Brown, who often defends the private sector and condemns the encroachments of government, be more generous in his charitable giving?

Between 2006 and 2010, Brown’s returns show, he never donated more than 2.7 percent of his large income to charity. Only in 2011, with a reelection battle looming, did he bump his giving up to 3.2 percent. No charitable gift is to be sneered at, of course. But countless Americans who earn far less than Brown give away a far higher share of what they do earn: On average, poor households contribute between 4 and 5 percent of their income to charity.

No one expects Brown to give the shirt off his back, or even to tithe – to give the tenth off the top that for many Americans is automatic. Yet a well-heeled Republican senator who believes in the efficacy of private action surely ought to be able to part with at least the same fraction of his income as the average poor giver does.

For Warren and Brown – for most of us – it’s easier to criticize other people’s standards than to faithfully measure up to our own. In the quest for votes, politicians will say just about anything to convince us they are worthy. The road to moral integrity isn’t paved with campaign sound bites, though, but with admirable behavior.

© Copyright 2012 Globe Newspaper Company