Free labor has the inspiration of hope; pure slavery has no hope. The power of hope upon human exertion, and happiness, is wonderful. The slave-master himself has a conception of it; and hence the system of tasks among slaves. The slave whom you can not drive with the lash to break seventy-five pounds of hemp in a day, if you will task him to break a hundred, and promise him pay for all he does over, he will break you a hundred and fifty. You have substituted hope, for the rod. And yet perhaps it does not occur to you, that to the extent of your gain in the case, you have given up the slave system, and adopted the free system of labor.

Fragmentary manuscript of a speech on free labor (17 September 1859?); Source: The Collected Works of Abraham Lincoln, ed. Roy P. Basler (1953), vol. 3, pp. 463–464

Collected Works of Abraham Lincoln. Volume 3.[quod.lib.umich.edu]