Robinson Crusoe, as we all know, took Friday as his slave.
Suppose, however, that instead of taking Friday as his slave,
Robinson Crusoe had welcomed him as a man and a brother, had read
him a Declaration of Independence, an Emancipation Proclamation and
a Fifteenth Amendment, and informed him that he was a free and
independent citizen, entitled to vote and hold office; but had at
the same time also informed him that that particular island was
his, Robinson Crusoe's, private and exclusive property. What would
have been the difference? Since Friday could not fly up into the
air nor swim off through the sea, since if he lived at all he must
live on the island, he would have been in one case as much a slave
as in the other. Crusoe's ownership of the island would be
equivalent to his ownership of Friday.
-- Henry George, 1883.