He identifies the sine qua non of thinking with what philosophers call intentionality, i.e. the aboutness of something. Computers, he argues, are incapable of manifesting intentionality and thus cannot think. After giving a brief description of what is called the "Turing Test" Egnor writes:
[W]e must first ask: what do we mean by "think"? We mean a mental act. What are the characteristics of a mental act? Several plausible characteristics have been proposed -- free will, restricted access (only the thinker experiences his thoughts), incorrigibility (only the thinker knows with certainty the content of his thought), qualia (raw sensory experience), etc. But philosophers agree that one unambiguous characteristic is essential to mental acts: intentionality.Why does this matter? Materialists wish to reduce the human person to the collection of chemical reactions which occur in his or her body and reduce all mental activity to computer-like processes in the brain. They wish to deny that there is anything to us other than the physical, but the facts of physics, as we pointed out last week, are proving to be formidable impediments to this project.
Intentionality is the other-directedness of a mental act. Intentionality is the "aboutness" of a thought. When I think about the weather, or about my boss, I'm thinking about something or someone other than my mental act itself. Things without minds don't have primary intentionality. A rock or a tree isn't intrinsically "about" something. A mental act can impart secondary intentionality to an object (that tree reminds me of spring), but the intentionality is imparted, not intrinsic. Only mental acts have intrinsic primary intentionality.
Computers certainly have secondary intentionality imparted to them by programmers and users. But to have a mind a computer would have to have primary intentionality. How would we know if a computer had primary intentionality? A computer's output would be intentional (in a primary sense) if the output were other-referential in a way that was not part of the program. Intentionality that was part of the program (the computer "talking about sports" because the programmer put "talk about sports" into the program) would of course merely be secondary intentionality -- the intentionality of the programmer imparted to the machine.
A "thinking" computer would have to talk about sports (or some other topic) that was not a part of its program. So primary intentionality would necessarily not be an algorithm of the computer. But an output by the computer that was not part of the computer's program wouldn't be computation. Computation is by definition bounded by an algorithm. Mental acts are not bound by an algorithm. If a computer were to manifest acts that were not algorithmic, it would be (in that respect) no longer a computer. No amount or ingenuity of programming can enable a computer to think. Mental acts are intrinsically non-computational.
The problems presented by human consciousness stubbornly resist the materialist's reductionism. The phenomena of consciousness - qualia, incorrigibility, intentionality - all suggest that the physical is not all there is to human persons.
One way to see this, perhaps, is to imagine a blind man who knows all the physical facts about red. He knows all the chemical reactions that occur in the brain when a sighted man sees red. There is nothing in the physical description of red that the blind man doesn't know, except he still does not know what red is. He doesn't know what it is like to experience red. There is something left over after all the facts about what happens in the brain when red is apprehended have been adduced.
In other words a complete physical description of red does not give us a complete description of red. There is, it seems, something non-physical involved in the sensation of seeing red, or tasting flavor, or hearing sound, or smelling frgarance.
One reason materialists are so reluctant to allow that there might be a non-material "substance" inhabiting the universe is that it's difficult to imagine how naturalistic evolution, which acts without purpose on material antecedents, could have produced an immaterial mind. The thought that we are more than just physical, material beings could lead to an openness to the possibility that the universe is underwritten, so to speak, by an intelligent mind that is the source of our minds, and that thought treads perilously close to the unwelcome conclusion, unwelcome for the materialist, that is, that the universe may be the handiwork of God.
