Descartes argued that that all humans had both a body and mind, and that the mind was eternal while the body was subject to physical and material laws. The universe was divided between the mind and matter, and the physical world could be explained by mathematical and scientific laws. Hobbes, Locke and other political and philosophical theorists of the 17th Century were also influenced by the new scientific thought of Descartes, Galileo and William Harvey to one degree or another, and had to incorporate them into philosophy (Ryle, p. 251). Ryle denied that any "ghost in the machine" existed, of that the immortal soul somehow operated the physical body. He admitted that explaining the link between bodies and minds was very difficult, although behaviorists had come to understand that expressions indicate moods and emotions, while vision, hearing and motion are all based on sensory inputs being received by the mind, but no one could actually measure and observe mental processes at the time Ryle was writing in 1949 (Ryle, p. 252). When people are described as knowing, believing, hoping or intending, these verbs certainly refer to internal mental processes, and from these philosophers constructed their theories of the mind. Ryle denies the existence of an eternal soul or mind separate from the body, even though he also concedes that "thinking, feeling, and purposive doing cannot be described solely in the idioms of physics, chemistry, and physiology" (Ryle, p. 255). Bodies and minds were part of a single whole, just as much as a college or department were all part of a university, even though the mind was a very special organ or machine that was like an internal motor within the body, it could still be understood by physical laws like cause and effect.
2) Ryle did not regard the mind as purely mechanical device, but as a complex organ that operated on the basis of cause and effect. If the mind was not a ghost or ethereal entity operating a body, it was more a kind of internal-governing motor of the body whose laws of operation were mostly unknown. These laws need not be purely deterministic, however, and Ryle rejected both idealism and materialism because they made an artificial distinction between the mind and body (Ryle, p. 257). Armstrong assumes that no better theory of the mind exists than the materialist or physicalist one, in which "man is nothing but a physic-chemical mechanism" (Armstrong, p. 259). Science cannot prove the existence of God or the immortal soul, but it offers "the best clue we have to the nature of man" even though that knowledge is a patchwork and far from complete (Armstrong, p. 260). Ryle attacked Descartes for arguing that the mind was a spiritual substance, and instead advocated behaviorism as an explanation for all mental processes (Armstrong, p. 260). For Armstrong, Ryle's behaviorism is not a satisfactory theory of the mind or consciousness, and speech and thoughts are not necessarily synonymous with behavior, but rather thought lies behind behavior (Armstrong, p. 261). Of course Armstrong is a materialist and as much of an opponent of dualism as Ryle, but his view of the mind seems more elusive and he regards it difficult to comprehend, at least with present-day scientific knowledge.
3) Armstrong argues that the mind is a complex physical-chemical organ and "stands behind and brings about our complex behavior," which is the product of certain mental states (Armstrong, p. 263). Human beings are undoubtedly conscious and have experiences, and these are not simply related to behavior (Armstrong, p. 264). Consciousness is an internal state, but also a physical state on the central nervous system, and concerns "simply the scanning of one part of our central nervous system by another" (Armstrong, p. 266). Nagel notes that science already has an excellent understanding about the physical functions of the human organism, including its anatomy and physiology, and intelligent bats and aliens might learn even more, even though they would have little basis for comprehending purely subjective and internal mental experiences in the human mind (Nagel, p. 314). Nagel finds it difficult to understand the "objective character of an experience apart from the particular point-of-view from which its subject apprehends it" (Nagel, p. 315). No one could comprehend the experience of a bat unless they could see the world from a bat's point-of-view. Physicalism has a clear meaning in that "mental states are states of the body; mental events are physical events" and they theory is not inadequate or unreasonable merely because we do not yet know how these states function (Nagel, p. 316). As a true science, physicalism is still in its infancy, just as nuclear physics would have been incomprehensible to philosophers 2,000 years ago. No one really knows today how mental and physical events could be the same phenomenon and other fields like physics, psychology, robotics and computer science can supply these answers. They still end up referring to mental events in subjective terms or they fail to make a real connection between the two (Nagel, p. 316).
4) Turing asks whether machines can think, and he believes they can, although not in same ways that the words 'machine' and 'thought' are conventionally defined (Turing, p. 285). No one in the 1940s and 1950s could have built an android body with skin that appeared human, although he did not rule out that science and technology would advance far enough to accomplish this in the future. Even so, a thinking machine would become no more human simply by "dressing it up in such artificial flesh" (Turing, p. 286). He imagined that in the future, machines would exist that could play chess or speak and understand English, and that it would also be able to learn in the same way that a child did (Turing, p. 287). Supposedly machines do not make mistakes, at least if they are correctly programmed and in proper working order, but a machine that never made an error "would be unmasked because of its deadly accuracy" (Turing, p. 293). Therefore, it would also have to be programmed to deliberately and 'knowingly' make mistakes, in order to conceal its machine nature.
Searle makes the distinction between weak and strong AI (Artificial Intelligence) in computer studies of the mid, asserting that strong AI theorists believe that the mind is a computer (and vice-versa) while weak AI finds that computers are useful for studying the mind in a "rigorous and precise fashion" (Searle, p. 298). He finds strong AI implausible except for those ideologically committed to the concept, since they tend to reduce the human mind to a system of symbol manipulation that can be programmed (Searle, p. 301). A computer could be programmed to communicate in Chinese and pass the Turing test since it would be understood by another Chinese speaker, although Searle also questions the adequacy of the Turing test itself (Searle, p. 302). Yale University theorists would counter that they could but a computer inside the head of a robot, and that it would not only perform formal symbol manipulation, but also walk, speak, eat, drink, drive a car or perform any other tasks its programmers assigned. It would see through television cameras in the eyes and generally think and act in a human -- or at least humanoid -- way, although Searle still doubts whether this simulated person would have intentionality (Searle, p. 303). Berkeley and MIT scientists thought they could design a computer that mimicked the neurons and synapses in the human brain, so that it would copy the actions in the brain of a Chinese speaker when it was read a story and asked questions about it. This mechanical or electronic brain would function exactly like that of a native Chinese speaker in its ability to process language and understand other inputs (Searle, p. 304).
5) Nagel rejects dualism in favor of physicalism, and regards the mind and body as part of a single whole, although like Armstrong he admits that science still finds mental processes mysterious. He also claims that subjective consciousness makes the problem of mind-body dualism "intractable" and that current reductionist and materialist theories cannot resolve it (Nagel, p. 311). He states that "we are completely unequipped to think about the subjective character of experience without relying on the imagination" but he had a solution to this problem of describing subjective mental states (Nagel, p. 317). He is a realist in his belief that the subjective domain existed as a fact in its own right, no matter whether humans will ever be able to explain or comprehend it adequately, and there may well be some facts that are simply never understood (Nagel, p 314). As a true science, physicalism was still relatively new, and it still lacked good models or even useful analogies for explaining the mind (Nagel, p. 316). Indeed, science still has a far better understanding of how bodies function rather than minds and mental states.