The chapter by Allen Newell, titled "Physical Symbol Systems," explores the fundamental concept of physical symbol systems (PSS) in the context of cognitive science. Newell argues that PSS is a crucial contribution of artificial intelligence and computer science to understanding the mind and intelligence. A PSS is a broad class of systems capable of manipulating symbols, which are hypothesized to be the same as the symbols humans use daily. The hypothesis posits that humans are instances of PSS, and thus, the mind enters the physical universe. Newell emphasizes the importance of restating and clarifying the concept of PSS, which has evolved over the past quarter century. He introduces an example system, SS (Symbol System), to illustrate the key property of universality, a constraint on the nature of mind-like systems. SS consists of memory, operators, control, input, and output, and can produce any input-output function, making it a universal machine. This universality is essential for an adaptive, intelligent system to cope with unknown environments. Newell discusses the challenges in defining universality, including the limitations of input and output domains, physical implementation limits, and the decomposition of input into instruction and input-proper. He also addresses the theoretical difficulties in achieving indefinite behavior and the existence of noncomputable functions. Despite these challenges, Newell demonstrates that SS can simulate any Turing machine, proving its universality. Finally, Newell generalizes the concept of PSS, stating that they are the same as universal machines and can produce any input-output function. This characterization provides a foundation for understanding the nature of mind and intelligence, emphasizing the importance of PSS in cognitive science.The chapter by Allen Newell, titled "Physical Symbol Systems," explores the fundamental concept of physical symbol systems (PSS) in the context of cognitive science. Newell argues that PSS is a crucial contribution of artificial intelligence and computer science to understanding the mind and intelligence. A PSS is a broad class of systems capable of manipulating symbols, which are hypothesized to be the same as the symbols humans use daily. The hypothesis posits that humans are instances of PSS, and thus, the mind enters the physical universe. Newell emphasizes the importance of restating and clarifying the concept of PSS, which has evolved over the past quarter century. He introduces an example system, SS (Symbol System), to illustrate the key property of universality, a constraint on the nature of mind-like systems. SS consists of memory, operators, control, input, and output, and can produce any input-output function, making it a universal machine. This universality is essential for an adaptive, intelligent system to cope with unknown environments. Newell discusses the challenges in defining universality, including the limitations of input and output domains, physical implementation limits, and the decomposition of input into instruction and input-proper. He also addresses the theoretical difficulties in achieving indefinite behavior and the existence of noncomputable functions. Despite these challenges, Newell demonstrates that SS can simulate any Turing machine, proving its universality. Finally, Newell generalizes the concept of PSS, stating that they are the same as universal machines and can produce any input-output function. This characterization provides a foundation for understanding the nature of mind and intelligence, emphasizing the importance of PSS in cognitive science.