Brown and Blue Eyed Slaves Puzzle.

A king has dominion over several islands each filled with slaves. The slaves have either blue or brown eyes. Some islands have just blue eyed slaves, some have just brown eyed slaves and some have a mixture of both.

The slaves on these islands are very smart and logical. Each has a burning ambition to be made free and travel to the mainland where the king and all the free people live.

The only way the slaves can become free is by deducing the colour of their own eyes and having done so they must depart the island that very day for the mainland on one of the many boats that go back and forth each day. This is not so easy as although the slaves can see the colour of everybody else's eyes, there are no reflective surfaces that allow them to see the colour of their own eyes. Additionally, slaves are never allowed discuss other slaves' eye colours so cannot tell or indicate in any way to another slave what eye colour that other slave has.

On one island there are just 3 slaves, all with blue eyes. One Monday morning, a king's official is visiting the island to check on things. Later that morning, as he is about to get on one of the many ferries back to the mainland, he is asked by the captain: "Does everyone on this island have brown eyes?". He answers: "No". Both the question and the response are overheard by the 3 slaves.

What, in the spirit of the question, happens that week on that island once the slaves hear this seemingly redundant information? Spirit of the question means to concentrate on what the slaves want to achieve because of their burning ambition and not on the normal mundane daily drudgery of slaves.

This was added to clear up some confusion about guessing from some original responders to this puzzle.

Slaves must at all times strive to logically determine what their eye colour is based on everything they know and having made the determination that they know without doubt what their eye colour is must leave for the mainland that same day otherwise they will be put to death as it is not allowed to remain on the island if you know your eye colour. If a slave boards the ferry to leave, he must explain to the captain his reasoning for assuming he now knows his eye colour. If the logic is incorrect or if the slave simply made a guess and cannot demonstrate any logic to his determination, then the slave will immediately be put to death.