Can machines think?
What is the measure of intelligence? And can an inanimate machine - however sophisticated - ever be said to be thinking for itself?
It's a question that has preoccupied computer scientists - and inspired science fiction writers - in equal measure.
But it wasn't until 1950 that we even had a definition of what constitutes independent thought by a machine. That was when Alan Turing, the father of modern computing who helped to break the enigma code at Bletchley Park during World War II, came up with a "test" to assess whether a computer was thinking for itself.
In the Turing Test a machine seeks to fool a group of judges into thinking they're holding a text based conversation with a person in another room. The idea is that if, after a five minute conversation and asking anything you like, you still can't tell you're talking to a machine then (to all intents and purposes) it can be said to be thinking for itself....the machine wins.
It's a feat no computer has yet managed, and I have to say I find it strangely reassuring that humour is usually the stumbling block. But on Sunday six Artificial Conversational Entities from all over the world will compete in the 18th Loebner Prize being hosted at the University of Reading.
Professor Kevin Warwick, who's organising this year's contest, believes it's only a matter of time before a machine beats the judges. We could even see more than one winner amongst this year's finalists, and if we do it would rank alongside Deep Blue's achievement in beating reigning world chess champion Gary Kasparov in 1997.
But even if a computer can hold up its end of a conversation for five minutes does that really constitute intelligence? The Turing Test seems to follow the logic that if something looks like a duck, swims like a duck, and quacks like a duck....then it must be a duck.
But can that really be said to be intelligent thought?
And what happens if one of the ACE's in this year's contest asks not to be switched off at the end of the conversation....would that be murder?