If this year's presidential campaign had a polarizing effect on the populace -- and by all accounts we're more divided than at any time since the Civil War -- then Steven Spielberg's "Lincoln" has arrived not a moment too soon.

The film makes us think about thinking. Lincoln's contemporary Karl Marx, a genius first and the father of communism second, marveled at the American president, describing him as that rare individual who is able to "succeed in becoming great without ceasing to be good." Kindness, fairness and clarity of thought were all wrapped up together in the character of Abe Lincoln.

Based partly on Doris Kearns Goodwin's book "Team of Rivals," "Lincoln" tells how the president masterminded passage of the 13th Amendment, which abolished slavery but fell short of granting blacks full equality. Its climax is Lincoln's eleventh-hour decision to delay peace talks with willing Confederate leaders until after the amendment had passed, a delay that implicitly sanctioned more misery and bloodshed.

In a darkened telegraph office, Lincoln weighs his decision to summon the Confederates or let them wait. He is bedeviled by two self-evident truths: the South's surrender would doom the amendment (its repatriated politicians would all vote "no"), and without slavery's abolition, the war would have been fought in vain.

Buying time, Lincoln engages in conversation with a telegraph operator trained in engineering. Surely the young man knows Euclid's "first common notion ... a rule of mathematical reasoning" that is "true because it works. Has done and always will do." Lincoln goes on in his slow, deliberate drawl: "It is a self-evident truth that things that are equal to the same thing are equal to each other."

The notion of equality had been as sacred as scripture to the founders. They considered it mathematically proven every time there was a fresh breakthrough in science because science itself was based on Euclid up to and including Newton's law of gravity. Proven also through engineering and architecture. Proven through courts of law. And proven through this American experiment with freedom.

Looked at this way, the choice was easy. "We began with equality -- that's the origin, isn't it?" Lincoln asks the operator. "That's justice."

Hilary Mantel's prize-winning novel "Wolf Hall," which chronicles the life of Thomas Cromwell, adviser to King Henry VIII, contains a strikingly similar moment. Like Lincoln, Cromwell (not to be confused with the Puritan revolutionary Oliver Cromwell) was an improbable leader, a homely man born to a blacksmith, slow-talking, self-taught in law and accounting, a consummate flip-flopper who deftly maneuvered between extreme poles of opinion for the sake of a greater good.

It was Catholic against Protestant then, and church against state. Cromwell became Henry's indispensable voice of reason. He weighed the pros and cons of every decision as if he were balancing the king's books, a task he undertook regularly and with scrupulous care. Euclid was his guiding light. Even as he earned the trust of hated adversaries, Cromwell leaned on self-evident truths to keep his eye on the ball. When did potential long-term gain justify short-term pain? What was the greater good?

For Lincoln, that ball was preserving the Union, which he had come to believe could only happen if slavery were destroyed. For Cromwell, it was keeping England from falling into chaos. In Mantel's account, Cromwell weighs his options as the king's resolve to remarry moves England closer to all-out war with the Vatican. At length, he shares with a trusted young accountant -- like Lincoln's engineer, a numbers man -- a treatise on proportion called Summa di Arithmetica, penned by a scholar who lived as a monk so that he could think in peace.

Brother Luca Pacioli studied proportion "in buildings, in music, in paintings, in justice, in the commonwealth, the state," Cromwell tells his protégé. He wrote "about how rights should be balanced, the power of a prince and his subjects, how the wealthy citizen should keep his books straight and say his prayers and serve the poor."

Cromwell adds: "Sometimes my friends in Italy send me poems ... but I think the poems are in here. ... Not that a page of figures is verse, but anything that is precise is beautiful, anything that balances in all its parts."

Perhaps we Americans should take a break from our bickering to think about those bedrock principles handed down from the ancients. What does justice actually mean? At what point does income inequality undermine national stability? Why are we threatened by scientific discovery? What are the underlying causes of conflict between governments and global capitalism? Are there no limits to growth in a finite world?

I wonder what would happen if, as Lincoln did in passing the 13th Amendment, our business and political leaders thought long and hard about self-evident truths, and, having done so, looked the future squarely in the eye.

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Bonnie Blodgett is a St. Paul writer. She blogs about gardening, politics and life at bonnieblodgett.com.