It is commonly asserted by pundits on the Democratic left that, sometime in the last century, the two parties switched sides. The Republicans became Democrats and the Democrats became Republicans. The point of this claim is to suggest that Lincoln was a progressive and that progressives today are the true inheritors of the Lincoln mantle.

The broader point is to rescue the Democratic Party from its own past and give Democrats today a "Get Out of Jail Free" card. According to this narrative, while the Democrats may have been the party of bigotry and oppression in the past, they are now the party of emancipation. And the Republicans have gone from being the good guys to being the bad guys.

These claims have the obvious disadvantage that they use language in a misleading way. Lincoln, for instance, repeatedly described himself as a conservative. The GOP, he said, was the conservative party while the Democrats were the radical pro-slavery party. Lincoln never used the term "progressive"; indeed the term wasn't coined until much later.

The issue, however, is not merely semantic. It involves the substantive issue of whether the two parties swapped ideologies and traded platforms. The left is basically saying that the cops became robbers and the robbers became cops. This seems implausible; did it really happen? We can resolve the question by performing the Lincoln test; that is to say, by examining the core philosophy of Abraham Lincoln, the first Republican president, and then seeing whether it is still the core philosophy of the GOP today.

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On multiple occasions, Lincoln defined slavery in this way: "You work; I'll eat." In his Chicago speech of July 10, 1858 Lincoln put it slightly differently, "You toil and I will enjoy the fruits of it." In its essence, Lincoln said, slavery gave men the right to "wring their bread from the sweat of other men's faces." As civil war historian Allen Guelzo points out, for Lincoln the most appalling feature of slavery was that it was a form of theft, theft of a man's labor.

Lincoln went on to argue that for centuries monarchs and aristocrats had stolen the labor of working people through a variety of mechanisms, from confiscatory taxation to outright confiscation. Lincoln insisted that, notwithstanding its lofty rationalizations, the Democratic slave plantation was based on this ancient principle of thievery. "No matter in what shape it comes, whether from the mouth of a king ... or from one race of men as an apology for enslaving another race, it is the same tyrannical principle."

Lincoln contrasted slavery with the Republican principle, which is that the hand that makes the corn has the right put the corn into its own mouth. In Lincoln's words, "As each man has one mouth to be fed, and one pair of hands to furnish food, it was probably intended that that particular pair of hands should feed that particular mouth." The social philosophy underlying this is that "every man can make himself" and "the man who labored for another last year, this year labors for himself, and next year he will hire others to labor for him."

Lincoln calls this the free-labor system, by which he means the free-market system. It operates on self-improvement, as Lincoln's own story illustrates. "I am not ashamed to confess that 25 years ago I was a hired laborer, mauling rails at work on a flat-boat." The free labor system, in Lincoln's words, "gives hope to all and energy and progress and improvement of condition to all."

Naturally, Lincoln says, people want to keep what they earn. "Even the ant who has toiled and dragged a crumb to his nest," he says, "will furiously defend the fruit of his labor against whatever robber assails him." And while the temptation to envious confiscation is inevitable, Lincoln told a delegation of workingmen during the Civil War, "Let not him who is houseless pull down the house of another, but let him labor diligently and build one for himself."

Failure to succeed, Lincoln said, is "not the fault of the system, but because of either a dependent nature which prefers it, or improvidence, folly or singular misfortune." As political scientist Harry Jaffa interprets Lincoln's words, "The brain surgeon and the street sweeper may have very unequal rewards for their work. Yet each has the same right to put into his mouth the bread that his own hand has earned. The brain surgeon has no more right to take the street sweeper's wages than the street sweeper to take the brain surgeon's."

Why not? Because for Lincoln such schemes of confiscation are a restoration of the slavery principle where "some have labored, and others have, without labor, enjoyed a large proportion of the fruits." Lincoln added, "This is wrong and should not continue. To secure to each laborer the whole product of his labor, or as nearly as possible, is a most worthy object of good government."

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Lincoln's philosophy can be seen in its practical implementation when his own stepbrother, age 37, wrote him to ask for a small loan to settle a debt. Lincoln responded, "Your request for eighty dollars, I do not think best, to comply with now." Lincoln reminded him this was not the first time he was being importuned for money; they had been down that road before. The problem, as he put it, is that the man was "an idler. You do not very much dislike to work; but you do not work much, merely because it does not seem to you that you could get much for it."

Here's what Lincoln proposed. "You shall go to work, tooth and nails, for somebody who will give you money for it." Lincoln added an incentive. "If you hire yourself at ten dollars a month, from me you will get ten more, making twenty dollars a month. ... Now if you will do this, you will soon be out of debt, and what is better, you will have a habit that will keep you from getting in debt again."

It should be obvious from this that there was no party switch between Republicans and Democrats. Lincoln's basic ideology that people have a right to the fruits of their labor, and that government, if it gets involved at all, should merely provide idlers and indigents with the means to become self-supporting, is even today the basic ideology of Republicans.

Moreover, it is equally clear that the confiscatory principle "You work, I eat" is even today the basic ideology of Democrats. The entire welfare state, from the New Deal through the Great Society to contemporary Democratic schemes, are all rooted in the same plantation philosophy of legally-sanctioned theft that Lincoln identified more than a century and a half ago.

Dinesh D'Souza's latest book, "Death of a Nation ," is published by St. Martin's Press. His movie of the same title is in theaters nationwide.