In an unsent 1860 letter, Abraham Lincoln mocked Sidney Fisher's claim that the “institution [of slavery] is a necessity imposed on us by the negro race.” And yet, Lincoln himself had often said that while slavery was an evil, the founders had to tolerate it where it existed owing to “necessity.” This raises the questions: What kinds of arguments about slavery and “necessity” did Lincoln find legitimate, and what kinds did he find to be illegitimate? In Lincoln's view, what exactly was it that necessitated the toleration of slavery where it existed at the time of the founding and into the 1850s? Lincoln's answers to these questions depart from the answers offered by Fisher, Thomas Jefferson, and Henry Clay; this departure helped pave the way not only to Lincoln's later embrace of emancipation, but also his eventual movement toward the position that African-Americans would and should be full citizens.