1860s, Letter to Alexander H. Stephens (1860) 
Context: The South would be in no more danger in this respect than it was in the days of Washington. I suppose, however, this does not meet the case. You think slavery is right and should be extended; while we think slavery is wrong and ought to be restricted. That I suppose is the rub. It certainly is the only substantial difference between us.
                                    
“One section of our country believes slavery is right and ought to be extended, while the other believes it is wrong and ought not to be extended. This is the only substantial dispute.”
            1860s, First Inaugural Address (1861) 
Context: One section of our country believes slavery is right and ought to be extended, while the other believes it is wrong and ought not to be extended. This is the only substantial dispute. The fugitive-slave clause of the Constitution and the law for the suppression of the foreign slave trade are each as well enforced, perhaps, as any law can ever be in a community where the moral sense of the people imperfectly supports the law itself. The great body of the people abide by the dry legal obligation in both cases, and a few break over in each. This I think, can not be perfectly cured, and it would be worse in both cases after the separation of the sections than before. The foreign slave trade, now imperfectly suppressed, would be ultimately revived without restriction in one section, while fugitive slaves, now only partially surrendered, would not be surrendered at all by the other. Physically speaking, we can not separate. We can not remove our respective sections from each other nor build an impassable wall between them. A husband and wife may be divorced and go out of the presence and beyond the reach of each other, but the different parts of our country can not do this. They can not but remain face to face, and intercourse, either amicable or hostile, must continue between them, Is it possible, then, to make that intercourse more advantageous or more satisfactory after separation than before? Can aliens make treaties easier than friends can make laws? Can treaties be more faithfully enforced between aliens than laws can among friends? Suppose you go to war, you can not fight always; and when, after much loss on both sides and no gain on either, you cease fighting, the identical old questions, as to terms of intercourse, are again upon you.
        
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Abraham Lincoln 618
16th President of the United States 1809–1865Related quotes
Reported in Nicholas Harris Nicolas, The Carcanet: a Literary Album, Containing Select Passages from the Most Distinguished English Writers (1828), p. 132.
2015, Remarks at Panama Civil Society Forum (April 2015)
                                        
                                        Progress In Religion (2000) 
Context: In the time of Jesus and for many centuries afterwards, there was a free market in human bodies. The institution of slavery was based on the legal right of slave-owners to buy and sell their property in a free market. Only in the nineteenth century did the abolitionist movement, with Quakers and other religious believers in the lead, succeed in establishing the principle that the free market does not extend to human bodies. The human body is God's temple and not a commercial commodity. And now in the twenty-first century, for the sake of equity and human brotherhood, we must maintain the principle that the free market does not extend to human genes. Let us hope that we can reach a consensus on this question without fighting another civil war.
                                    
Quoted in Jilly Cooper and Tom Hartman, Violets and Vinegar, "The Battle Done," (1980)
2000s, The Real Abraham Lincoln: A Debate (2002), The Right of Secession Is Not the Right of Revolution