November 1st, 2009


I was cleaning up some old junk from boxes in my house, and came across this puzzle I was given in 1993.

Once upon a time, there lived 800 green-eyed people and 200 blue-eyed people on an island. No one on the island knew their own eye color, nor did they know the exact number of blue and green eyed people on the island. There was a local taboo against talking about eye color (which the citizens never violated), and there were no reflective surfaces on the island. There were absolutely no physical means for a person to determine his or her own eye color. The citizens on this island were all firmly committed to the belief, however, that if a person could figure out that he or she had blue eyes by using logic, the person had to commit suicide at midnight of that day.

Every day at noon, the citizens met in the town square to stare lovingly into each other's eyes. All was happy and gay. Then one day, day 0 to be exact, an oracle descended upon the island from the heavens and announced during the noontime meeting, "There are blue-eyed people on this island." The citizens promptly stoned and killed the oracle.

What happened after that day, and why? (Notice that the oracle said something all the citizens already knew.)

Enjoy. :)