Propositions of Lincoln

I have never had a feeling politically that did not spring from the sentiments embodied in the Declaration of Independence — Abraham Lincoln


“The proposition that all men are created equal,” President Abraham Lincoln said was the reason that inspired the American forbears to declare independence four score and seven years earlier. His remarks on the afternoon of Thursday, November 19, 1863 were attending the dedication of the Soldiers’ National Cemetery.1

“Now,” Lincoln said, raising his voice, “We are engaged in a great civil war, testing.” Two years later, in his second inaugural address, characterized as the only speech worthy of comparison to the remarks made at Gettysburg, Lincoln famously admitted that the test of slavery was “the cause of the war.” 2

The Problem

Despite the reasoning Lincoln seemed to communicate so effortlessly throughout his career, one might question a statement released during his first presidential campaign – he had “nearly mastered the six books of Euclid,” referring to the ancient mathematician credited with discovering geometry through a collection of books entitled the “Elements,” about elementary geometry and its underlying logic.

With a close reading of the Gettysburg Address in light of Lincoln’s claim, there remains little doubt that he may have been able to suggest a more persuasive argument against slavery, had he applied the same logic of Euclidean geometry that he claimed in a campaign biography to have studied.3

The Evidence

Lincoln wrote a letter on April 6, 1859 to decline an invitation for a Boston celebration in honor of Thomas Jefferson’s birthday.

After explaining how prior engagements would keep him from attending, Lincoln wrote about the irony of the celebration being held in the same city that was once headquarters to the Federalists that opposed Jefferson.

Lincoln continued by relating Jefferson’s standards for the nation in terms of the math developed by Euclid, even going so far as to write that “the principles of Jefferson are the definitions and axioms of a free society.” 4

Euclidean Logic

The language of Euclid’s math described by Lincoln refers to definitions that make terms explicit and self-evident postulates, which are axioms that are automatically accepted as being true.

Practical examples include Euclid’s Definition #3 stating that points are the ends of a line and Postulate #1 that says given any two points such as A and B, there is a line AB which has them as endpoints.

Through deductive reasoning, one can prove a given proposition as either true or false through the utility of supporting axioms, definitions, and other propositions that have been proven as true.

Unlike axioms, propositions are statements that first need to be proven as true before they can be of any use. By their very definition, propositions are subject to proof through testing based on self-evident postulates (i.e., axioms).5

Common Sense

Why did Lincoln at Gettysburg argue that the statement “all men are created equal” was a proposition being tested if it was instead an axiom postulated in Declaration of Independence as self-evident and thus automatically true?

One possible explanation is that by speaking to a different level of certainty, Lincoln was able to shift his trajectory from past ideas to present realities.

But his letter about the Boston celebration revealed a capacity for him to have utilized all of Jefferson’s self-evident postulates in the Declaration of Independence in support of his arguments to preserve the Union, while at the same time working to abolish slavery.

Lincoln’s letter ended with him praising the personal qualities of Jefferson, who himself said of Euclid’s logic that “there is scarcely a day in which he will not resort to it for some of the purposes of common life.” 6


1. “The Heroes of July,” The New York Times, November 20, 1863.  Drew Gilpin Faust, This Republic of Suffering: Death and the American Civil War (New York: Knopf, 2008), 69.

2. Garry Wills, Lincoln at Gettysburg: The Words That Remade America (New York: Simon & Schuster, 1993), 189. Roy P. Basler, ed., The Collected Works of Abraham Lincoln, 9 vols. (New Brunswick: Rutgers University Press, 1953-1955), 7:23.  Ibid., 8:332.

3. Ibid., 4:62.

4. Ibid., 3:374-376.

5. Thomas L. Heath, trans., The Thirteen Books of Euclid’s Elements, Vol. 1: Books 1-2 (New York: Dover, 1956), 153-155.

6. Barbara B. Oberg, ed., The Papers of Thomas Jefferson, 36 vols. (Princeton: Princeton University Press, 2004), 31:126.


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