If a robot is produced that behaves just like one of us in all respects, including thought, is it conscious or just a clever machine, asks Prof Barry C Smith, director of the Institute of Philosophy.
Human beings are made of flesh and blood - a mass of brawn and bone suffused with an intricate arrangement of nerve tissue. They belong to the physical world of matter and causes and yet they have a remarkable property - from time to time they are conscious.
Consciousness provides creatures like us with an inner life: a mental realm where we think and feel and have the means to experience sights and sounds, tastes and smells by which we come to know about the world around us. But how can mere matter and molecules give rise to such conscious experiences?
The 17th Century French philosopher, Rene Descartes, thought it couldn't. He supposed that in addition to our physical make-up, creatures like us had a non-material mind, or soul, in which our thinking took place.
For Descartes, the non-material mind was uniquely human. He denied that animals had minds.
Descartes denied animals had minds
When they squealed with what we considered to be pain this, he thought, was just air escaping from their lungs. Animals were mere mechanisms. And even if we created a clever mechanical doll that replicated all our movements and reactions, it would not be capable of thinking because it would lack the power of speech.
These days few of us would deny our animal natures or accept that all other animals lacked consciousness. Besides, the idea of an immaterial soul makes it hard to understand how the mental world could have any effect on the physical world, and for that reason many contemporary philosophers reject mind-body dualism.
How could something that had no material existence move our limbs and respond to physical inputs. Surely it is the brain that is responsible for controlling the body and so it must be the brain that gives rise to our consciousness and decision making. And yet many of the same thinkers would agree with Descartes that no machine could ever be conscious or have experiences like human beings.
Carbon creatures
We can no longer rely on Descartes' criterion for deciding which beings could think. Nowadays computers can make use of language and synthesised speech improves all the time. It was the potential for computers to use language and respond appropriately to questions that led Alan Turing, the mathematician and war time code-breaker, to propose a test for machine intelligence.
Turing developed a test for machine intelligence
He imagined a person sitting in a room, communicating by computer screen with two others in different rooms. She could type in questions and receive answers, and if she could not tell which of the respondents was a person and which was a computer she had no reason to treat them differently.
If she was prepared to treat one as intelligent, she should be prepared to treat the other as intelligent too. This is known as the Turing Test, and if the situation is arranged carefully, computer programs can pass it.
The original Turing Test relies on not being able to see who is sending the replies to questions, but what if we extended the test and installed the computer programme in a life-like robot? Robotics have developed rapidly in the last decade and we now see machines that move and behave like humans. Would such a display of life-like behaviour combined with appropriate responses to questions convince us that the machine was not only clever but also conscious?
Here, we need to draw a distinction between our thinking that the robot was conscious and it actually being conscious. We may be tempted to treat it as a minded creature but that doesn't mean it is a minded creature.
Last mystery
Those who study machine consciousness are trying to develop self-organising systems that will initiate actions and learn from their surroundings. The hope is that if we can create or replicate consciousness in a machine we would learn just what makes consciousness possible.
Researchers are far from realising that dream and a big obstacle stands in their way. They need an answer to the following question - could a silicon-based machine ever produce consciousness, or is it only carbon creatures with our material make-up that can produce the glowing technicoloured moments of conscious experience? The question is whether consciousness is more a matter of what we do or what we are made of.
Consciousness may be the last remaining mystery for science, but to some extent it has been dethroned from the central role it used to occupy in the study of the mental. We are learning more and more from neuroscience and neurobiology about how much of what we do is the result of unconscious processes and mechanisms.
And we are also learning that there is no single thing consciousness is. There are different levels of consciousness in humans, and much of our thinking and decision making can go on without it.
It's worth remembering that the only convincing experience of consciousness we have is our own. We are each aware of our own inner lives, but have only indirect access to the inner mental lives of others. Are the people around me really conscious in the way I am, or could they all be zombies who walk and talk and act like humans although there is nobody home.
And this is creates a twist in our story. For if we managed to produce a robot that behaved just like one of us in all respects that might be a proof not of the consciousness of a robot or machine, but instead may be a convincing demonstration of how much we could manage to do without consciousness.
What are your views on this?
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