By no means the least interesting of the many points touched in these debates is Lincoln’s own estimate of the probable duration of slavery, or rather of the least possible period in which “ultimate extinction” could be effected, even under the most favorable circumstances.

  [Sidenote] Lincoln-Douglas Debates, p. 157.

Now, at this day in the history of the world [said he, in the Charleston debate], we can no more foretell where the end of this slavery agitation will be than we can see the end of the world itself.  The Nebraska-Kansas bill was introduced four years and a half ago, and if the agitation is ever to come to an end, we may say we are four years and a half nearer the end.  So too we can say we are four years and a half nearer the end of the world; and we can just as clearly see the end of the world as we can see the end of this agitation.  The Kansas settlement did not conclude it.  If Kansas should sink to-day, and leave a great vacant space in the earth’s surface, this vexed question would still be among us.  I say then there is no way of putting an end to the slavery agitation amongst us, but to put it back upon the basis where our fathers placed it, no way but to keep it out of our new Territories—­to restrict it forever to the old States where it now exists.  Then the public mind will rest in the belief that it is in the course of ultimate extinction.  That is one way of putting an end to the slavery agitation.

The other way is for us to surrender and let Judge Douglas and his friends have their way and plant slavery over all the States; cease speaking of it as in any way a wrong; regard slavery as one of the common matters of property and speak of negroes as we do of our horses and cattle.  But while it drives on in its state of progress as it is now driving, and as it has driven for the last five years, I have ventured the opinion, and I say to-day that we will have no end to the slavery agitation until it takes one turn or the other.  I do not mean to say that when it takes a turn towards ultimate extinction it will be in a day, nor in a year, nor in two years.  I do not suppose that in the most peaceful way ultimate extinction would occur in less than a hundred years at least; but that it will occur in the best way for both races, in God’s own good time, I have no doubt.

But the one dominating characteristic of Lincoln’s speeches is their constant recurrence to broad and enduring principles, their unremitting effort to lead public opinion to loftier and nobler conceptions of political duty; and nothing in his career stamps him so distinctively an American as his constant eulogy and defense of the philosophical precepts of the Declaration of Independence.  The following is one of his indictments of his political opponents on this point: 

  [Sidenote] Lincoln-Douglas Debates, p. 225.