It was an open letter. Mr. Greeley had evidently lost sight of his economic theories as applied to slavery in the abstract, and now, as a practical philosopher, caught hold of the question by the handle. Mr. Lincoln replied within a few days, but was still joined to his abstract theories of constitutional law. He loved the Union, and all he should do for the slave should be done to help the Union, not the slave. He was not desirous of saving or destroying slavery. But certainly he had spoken more wisely than he knew when he had asserted, a few years before, that "a nation half free and half slave, could not long exist." That was an indestructible truth. Had he adhered to that doctrine the way would have been easier. In every thing he consulted the Constitution. His letter is interesting reading. "EXECUTIVE MANSION, WASHINGTON,} "August 22, 1862.} "Hon. HORACE GREELEY: "_Dear Sir_: I have just read yours of the 19th instant, addressed to myself through the New York Tribune. "If there be in it any statements or assumptions of fact which I may know to be erroneous, I do not now and here controvert them. "If there be any inferences which I may believe to be falsely drawn, I do not now and here argue against them. "If there be perceptible in it an impatient and dictatorial tone, I waive it in deference to an old friend whose heart I have always supposed to be right. "As to the policy 'I seem to be pursuing,' as you say, I have not meant to leave any one in doubt. I would save the Union. I would save it in the shortest way under the Constitution. "The sooner the national authority can be restored, the nearer the Union will be the Union as it was. "If there be those who would not save the Union unless they could at the same time save slavery, I do not agree with them. "If there be those who would not save the Union unless they could at the same time destroy slavery, I do not agree with them. "_My paramount object is to save the Union, and not either to save or destroy slavery._ "If I could save the Union without freeing any slave, I would do it; if I could save it by freeing all the slaves, I would do it; and if I could do it by freeing some and leaving others alone, I would also do that. "What I do about slavery and the Colored race, I do because I believe it helps to save this Union; and what I forbear, I forbear because I do not believe it would help to save the Union. "I shall do less whenever I shall believe what I am doing hurts the cause; and I shall do more whenever I believe doing more will help the cause. "I shall try to correct errors when shown to be errors; and I shall adopt new views so fast as they shall appear to be true views.