There is no end to the flow of books written about Abraham Lincoln. But Allen Guelzo's 1999 book, Abraham Lincoln: Redeemer President, is a solid part of the canon. An intellectual biography of Lincoln, the book won the Lincoln Prize for 2000 and the 2000 Book Prize for the Abraham Lincoln Institute. Guelzo won both prizes again in 2005 for Lincoln's Emancipation Proclamation: The End of Slavery in America.

Now Guelzo has followed up with Abraham Lincoln as a Man of Ideas (Southern Illinois University Press, 2009), a collection of essays on key (and sometimes conflicting) aspects of Lincoln's thought. From 1998 to 2004, Guelzo was the dean of the Templeton Honors College at Eastern University. Since 2004 he has been the Henry R. Luce Professor of the Civil War Era at Gettysburg College.

In the introduction to Abraham Lincoln as a Man of Ideas, you write about the way people frequently ask, "What would Lincoln do?" WWLD, if you will. Given the tremendous technological, political, and cultural gap between Lincoln's time and ours, how realistic is it to ask that question?

It's not realistic at all.The interest in WWLD is more metaphorical, more a matter of character questions. People are really asking what kind of a person Lincoln was. When we see intractable political or economic problems, we want those traits to be deployed and to succeed in the same way that Lincoln succeeded in facing the Civil War.

Since Lincoln was not a religious believer in the way that most other Christians of his time were, where did Lincoln's morality come from?

It came from a number of sources, the most important of which is natural law theory. But Lincoln, not a professional philosopher, dabbled in a number of systems or theories about virtue. He didn't really feel under any particular compulsion to be completely consistent in how he used them.One part of Lincoln embraced utilitarian ethics. And I literally mean utilitarian in the sense of 19th-century British liberal utilitarianism.

"The greatest good for the greatest number"?

Exactly. He even quotes that line of Bentham's. And we know that Lincoln read very extensively in liberal Utilitarians like John Stuart Mill. In one of Lincoln's most famous descriptions of the ideal economy, he says that the prudent penniless beginner works for someone else, then the next year, having saved that money, he works on his own account, and then the year after that he's acquired so much success he hires someone else. Lincoln says that's the ideal system.

From his earliest entrance into politics in the 1830s until the mid 1850s, Lincoln is dealing pretty much on the basis of liberal utilitarianism. But when he encounters the slave crisis, he has to find another base from which to operate, because liberal utilitarianism's fixation on nonmoral considerations—on property rights, on economics, as the basis for understanding human relations—didn't offer a very stable ground from which to criticize slavery. In searching for an alternative ground on which to base his opposition, Lincoln started reaching for natural law.

That's significant for the religious part because the moment he does that, he steps into a circle that is shared widely in the 19th century in America by religious thinkers. The founding of the American republic is very much an epoch in the Enlightenment. And in the 1780s and 1790s, that meant the marginalization of religion, which in this case, really, was Christianity.

How do you get belief out of the prison of these marginalized religious institutions and back on the public square? The method for doing that is natural law because Christianity certainly had a long record of appealing to natural law as being the same message as that which is preached by Christian revelation. The one is natural revelation; the other is special revelation.This became a default position for American religious figures who no longer could get the attention of the American system by appealing to divine revelation.To appeal instead to natural revelation is not denominational, it's not institutional, and it's something that can appeal to everyone because the Enlightenment itself did a lot with natural law. With Lincoln appealing to natural law as a basis to oppose slavery, he suddenly finds himself standing side by side with Christian thinkers who are preaching natural law.

And he uses God language to do that.

Oh yes, he does. Talking about God is part of the overall constellation of natural law thinking.In natural law you talk about Nature and Nature's God, but if you're not watching the little cups on table, you can switch these around and suddenly that can become Christian God too.And that creates a commonality that puts Lincoln in the 1850s much closer to religious language and religious thinking than he was in his green and salad Utilitarian days.

Lincoln didn't believe in moderation, middle-of-the-roadism, or compromise. But he did believe in the virtue of prudence. What is that exactly?

Moderation is a passive, tragic point of view. Moderation suggests that we really cannot reconcile the conflicting situations we're find ourselves in. So we have to take a bit of this and a bit of that and hope that somehow they will cohere. Lincoln was instead about prudence. Prudence is ironic rather than tragic. It is ironic because it understands that there are unintended consequences of your actions, and therefore you have to chart your path toward your goal with exquisite care, having full regard for the integrity of means as well as the integrity of ends.

But charting your course toward your goals is difficult when you believe that there will be unintended consequences.

Exactly. It makes you aware that you may not be perfect. The immediatists of Lincoln's day, the abolitionists, were perfectionists. As the heirs of Jonathan Edwards and the Awakenings, these people knew exactly what the answers were even before the questions were asked. They thought you didn't waste time abolishing slavery any more than you waste time calling people to the anxious seat.The whole reason you've got the anxious seat is that you want an immediate response. That was the genius of Finney's preaching. The abolitionists are a marvelous echo of that because they despised anything that was not an immediate, fully virtuous response.

Lincoln hasn't got any time for those people or any other kind of reform movement. As early as the 1840's in talking about temperance reform, he puts all of his chips on the Washingtonian Temperance Society—a secular alternative to most temperance organizations in the country. Lincoln would not have been sympathetic to Cary Nation. He favored the Washingtonians because they were gradualists.They believed in reasoning with people. They were aware of the possibility of unintended consequences. And he carried that attitude over to the abolitionists.

Abraham Lincoln is not a revivalist.And here is the third factor that comes into the making of his religious geography—the ancestral burden of Calvinism. His parents are members of the Separate Baptists, who are absolute, utter predestinarians. Even after he has long since untied himself from the explicit dogmas of Calvinism, the mental habit of fatalism and determinism sticks with him.

Lincoln wants nothing to do with revivalism because that smacks too much of the self-actuated will. He doesn't believe that people can change themselves. You have to offer them motives. As soon as I say motives, we're in bed with utilitarianism. See how this circle of ideas works in Lincoln's mind.It's not philosophically coherent but each of those clusters of ideas, Utilitarianism, Natural Law, Calvinism, each of them has a valence with each other.

So he didn't believe that people could change themselves, and yet as a Whig, he thought that people could be definitely motivated to achieve and run after rewards.

Exactly.You respond not because of the self-actuating will, but because of motives appealing to your self-interest. So what is important as a Whig is to dangle the appropriate motives in front of people. This is how he explains the process of emancipation. In the letter he writes to James Conklin in September 1863, he speaks about black soldiers. He says, you people who are criticizing the war and emancipation, you would like the war to be won, yes?And everyone says yes, and then he says, Well don't you imagine that emancipating blacks and making them soldiers is going to help us win the war? And they say, a little less enthusiastically, uh, yes. Well, you have to offer them motives, because Negroes, like all other people, act upon appeals to their self interest. So you have to dangle the greatest motive, freedom, out there, and they will enlist and help win the war.

You say the Lincoln was opposed to slavery on principle. But you also say that his hatred for slavery was very subjective. Was this the public Lincoln versus the private Lincoln?

Yes. Publically, he offers a variety of reasons for opposing slavery.A lot of them are linked to natural law considerations in contrast to Steven A. Douglas's appeal to simple, raw, white majoritarianism. Privately, other things are burning inside Lincoln that are spin offs from personal experience. One personal experience, certainly, is his antagonistic relationship with his father and the experience of always having his father appropriate the wages that were paid to him. Lincoln later described his early youth by saying, "I was once a slave." Lincoln conceived of slavery as any condition of economic seizure or confiscation of the fruits of someone's labor. And that is the real fundamental origin of his opposition to slavery. It's not a matter of racial empathy. A certain element of that later begins to work on Lincoln. But for much of his life, the origins of his opposition to slavery are not cerebral. They are not theoretical. They really are rooted in this very raw sense of indignation that he worked and someone else got the benefit.

Thank you very much for giving us a great book.

The cherry on top is the book jacket, because that portrait of Lincoln by W. B. Traverse, a European artist, painted from life, has never been reproduced.

It is privately owned. I'm not even allowed to tell you the identity of the private collector. The owners of the painting really don't want a stampede of people coming to see this portrait.

This particular portrait had taken my attention many years before when I saw a black-and-white reproduction in a magazine, because it captures the man's intellectual curiosity.So often the image we have of Lincoln is this simple, honest country bumpkin. He let people think that way because they would underestimate him. But Leonard Swett, one of Lincoln's legal associates on the 8th judicial circuit said that anybody who took Abraham Lincoln for a simple-minded man would soon wake up with his back in a ditch.

I love the way that portrait captures Lincoln's sharp, shrewd curiosity. It was so lifelike in capturing the man that when the painting was unveiled, Mary Todd Lincoln fainted from the shock of seeing it. It was him, and it is very rare that a photograph or a portrait completely captures Abraham Lincoln. He was such an elusive character.