Physical Symbol System Hypothesis Gagan Deep Kaur Roll No Course Seminar - CS 344

Physical Symbol System A PSS consists of - Symbols - set of entities that are physical patterns - Symbol Structures - number of instances/tokens related in some physical way - Processes – operate on these expressions to produce other expressions

S6 S5 S4 S3S2 S1 Symbol Structures - “Expressions” S1 CC$7899ABVV

S6 S5 S4 S3S2 S1 Collection of “Expressions” S12 S11S10 S9S8 S7 S18S17S16S15S14S13 S24S23S22S21S20S19 S30S29S28S27S26S25 At any given time, a PSS contains - collection of expressions - processes to operate on these expressions creation, modification, reproduction, destruction

Physical Symbol System Key Concepts Designation – the symbol/expressions can refer to something else. Interpretation – the expressions can refer to its own computational processes which the system can evoke and execute

Examples of Symbol Systems SystemSymbolExpressionsProcesses LogicAnd, Or, Not,Propositions (T/F)Rules of Inference Algebra+, -, *, /, y, z, 1, 2, 3…. Equations (2+3=5) Rules of Algebra Digital Computer0, …..Program -----ChessChess PiecesPosition of pieces on the board Legal Chess Moves

Physical Symbol System Hypothesis - By Allen Newell and Herbert Simon “A physical symbol system has the necessary and sufficient means for general intelligent action”

Claims - Human thinking is a kind of symbol manipulation - Symbol manipulation necessary for intelligence - Machines can be intelligent, because - Symbol manipulation is sufficient for intelligence Core assumption of Strong AI

Grounds of PSS Brain similar with a physical symbol system Psychological Experiments – decision making, learning processes Running AI programs –chess, checkers, theorem proving, Clark – Productivity of Human Thoughts

Examples of PSS SystemSymbolExpressionsProcesses Digital Computer0, …..Program -----ChessChess PiecesPosition of pieces on the board Legal Chess Moves BrainEncoded in brainThoughtsMental Operations like thinking AI ProgramData

Merits Computationally possible to encode symbolic human knowledge Opened avenue for machine intelligence!

Implications Appropriately programmed computer is capable of conscious thought Machines can be made to think and have genuine understanding Can Physical Symbol Systems Think?

symbol manipulation = intelligence?

Critiques Serial manipulation of ≠ parallel and distributed discrete symbols processing (PSS) (Human Brain) Dreyfus – Role of unconscious instincts than conscious symbol manipulation

Searle’s Chinese Room

Intelligence requires Understanding. Does the program understands the symbols that it uses? Does “symbols” have any meaning for the machine?

Conclusion The question thus boiled down to this: Could a system think or understand just by having right sort of program? Is syntax enough to ensure “semantics” which is necessary for understanding.

Can Physical Symbol System be Intelligent?

References Clark, Andy, “Philosophical Implications”, Artificial Intelligence, Ed. Margaret Boden, Academic Press, California, 1996 Dreyfus, Hubert, What Computers Can’t Do: The Limits of AI, Harper & Row, New York, 1979 Newell, Allen and Simon, Herbert, “Computer Science and Empirical Inquiry: Search and Symbols”, Mind Design II, Ed. John Hagueland, MIT Press, 1997, Searle, John, “Minds, Brains and Programs”, Minds I, Ed. Douglas Hofstadter, and Daniel Dennett, Basic Books, 2001, P Wikipedia, Stanford Encyclopedia Various Internet Sources For The Pictures!