noun: The tendency of things, beliefs, etc., to change into their opposites.
ETYMOLOGY: From Greek enantio- (opposite) + dromos (running). Earliest documented use: 1917.
NOTES: You can keep going up a mountain, but once you hit the peak you can only go down. A pendulum moves in one direction, but once it has reached its rightmost it travels left. So it goes with beliefs, ideologies, and politics, apparently. Once we have elected a black man as a president, we have to pick someone with a long sordid record of discrimination.
original at DW