Computer Science as Empirical Inquiry Instructor: Viola Schiaffonati April, 19th 2012 Computer Science as Empirical Inquiry: Symbols and Search (Newell e Simon 1976) Herbert Simon Philosophical Topics of CS Allen Newell 2 An empirical discipline 3 “Computer science is an empirical discipline. We would have called it an experimental science, but like astronomy, economics, and geology, some of its unique forms of observation and experience do not fit a narrow stereotype of the experimental method. None the less, they are experiments. Each machine that is built is an experiment. Actually constructing the machine poses a question to nature; and we listen to the answer by observing the machine in operation and analyzing it by all analytical and measurement means available. Each new program that is built is an experiment. It poses a question to nature, and its behavior offers clues to an answer. Neither machines nor programs are black boxes; they are artifacts that have been designed, both hardware and software, and we can open them up and look inside.” Philosophical Topics of CS 4 Basic science Computer science as experimental science New machines and programs as experiments Analysis of the answer given by the nature Relation between structure and behavior of machines and programs Possibility to learn by a single experiment Flaws of a program detected by a single inspection Computer science as basic science to discover new phenomena and to analyze known phenomena New understanding by means of empirical research Example: development of the notion of a symbolic system Philosophical Topics of CS 5 Symbols One of the fundamental contributions to knowledge of computer science: to explain what symbols are This explanation is a scientific proposition about Nature Proposition empirically derived with a long and gradual development Symbols lie at the roots of intelligent action The ability to store and manipulate symbols is one of the structural requirements for intelligence Philosophical Topics of CS Physical Symbol System 6 Set of entities (symbols) that can occur as components of another type of entity (expressions o symbol structures) Symbol structure composed of a number of instances of symbols related in some physical way At any instant of time the system will contain A collection of these symbol structures A collection of processes that operate on expressions to produce other expressions (creation, modification, reproduction, and destruction) Physical symbol system is a machine producing through time an evolving collection of symbol structures It exists in a world of objects wider than symbolic expressions Philosophical Topics of CS Symbols and expressions 7 Letters are symbols and words are expressions or symbol structures Words are symbols and sentences are expressions or symbol structures Philosophical Topics of CS 8 Designation A expression designates an object if, given the expression, the system can Affect the object itself Behave in ways dependent on the object Essence of designation To access to the object via the expression Philosophical Topics of CS 9 Interpretation The system can interpret an expression if The expression designates a process and The system can carry out the process Essence of interpretation Given an expression the system can perform the indicated process Philosophical Topics of CS Additional requirements 10 Arbitrariness A symbol may be used to designate any expression There exist processes for creating any expression and for modifying any expression in arbitrary ways Potentiality: there exist expressions that designate every process of which the machine is capable Stability: once created expressions will continue to exist until explicitly modified or deleted Unboundness: the number of expressions that the system can hold is unbounded Philosophical Topics of CS Physical symbol system and computer science 11 Physical symbol system bears a strong resemblance to all general purposes computers Defining features To produce through time an evolving collection of symbol structures To read, recognize, and write symbols To communicate symbols from a a part of the system to another part to specify and control the activity performed Philosophical Topics of CS Why ‘physical’? 12 The adjective ‘physical’ denotes two important features These systems obey to the laws of physics – they are realizable by engineered systems made of engineered components The term symbol is not restricted to human symbol systems Philosophical Topics of CS Physical Symbol System Hypothesis “A physical symbol system has the necessary and sufficient means for general intelligent action” Philosophical Topics of CS 13 … necessary means … 14 Any system exhibiting general intelligence will prove upon analysis to be a physical symbol system Philosophical Topics of CS … sufficient means … Any physical symbol system of sufficient size can be organized further to exhibit general intelligence Philosophical Topics of CS 15 … general intelligence action 16 “By general intelligent action we wish to indicate the same scope of intelligence as we see in human action” Within some limits of speed and complexity Behavior appropriate to the ends of the system Behavior adaptative to the demands of the environment Philosophical Topics of CS Some consequences of the hypothesis 17 Symbolic capacity (to store and manipulate symbols) as the basis of intelligent behavior Physical symbol system as an instance of a universal machine (general purpose computers) Intelligent action performed by a system able to execute exclusively algorithmic procedures Philosophical Topics of CS Other consequences 18 Human beings have the features of physical symbol systems Human intelligent action can be modeled by a system able to manipulate symbols Intelligence and biology Our human wetware is not so special Intelligence can be implemented on other ‘platforms’ Philosophical Topics of CS Intelligence and symbols manipulation Gottfried W. Leibniz and the calculus ratiocinator (1666) Thomas Hobbes and the theory of reasoning as theory of adequate combinations (1655) Philosophical Topics of CS 19 How to prove the hypothesis? 20 Law of qualitative structure It specifies a general class of systems within which those capable of intelligent action Empirical hypothesis than can be prove or refute only ‘on the field’ (not a theorem) How to carry out its defense Construct-and-test paradigm Philosophical Topics of CS Two types of empirical evidence 21 To prove that the hypothesis is sufficient To try to realize a system able to manipulate symbols Artificial Intelligence To prove that the hypothesis is necessary To check to have a physical symbol system ever time there is intelligence Cognitive psychology Philosophical Topics of CS Negative evidence No alternative hypotheses to the physical system hypothesis (by 1976!) 22 Neither behaviorism nor Gestalt theory This is seen as a proof of the necessity of the symbolic paradigm Philosophical Topics of CS Strong computationalism 23 Physical symbol system as the computational model of human cognitive processes Human cognitive activity can be simulated by a computational process Human cognitive activity consists of symbols manipulation Philosophical Topics of CS 24 Critical issues Hypothetical character of the connection between intelligence and symbol systems Qualitative characterization of the physical symbol system hypothesis: any logical demonstration, but only some sort of empirical evidence Demonstration based on the evidence that an alternative paradigm does not exist, not on the evidence than an alternative paradigm cannot exist Philosophical Topics of CS Role of hypothesis in computer science Physical Symbol System Hypothesis to illustrate concretely that computer science is a scientific enterprise 25 It develops scientific hypotheses which it then seeks to verify by empirical inquiry Substantial scientific hypothesis representing an important discovery of computer science and a strong impact on the field Philosophical Topics of CS 26 References Newell, A., Simon, H. (1976) “Computer Science as Empirical Inquiry: Symbols and Search” Communications of the ACM, 19:3, 113-126 Philosophical Topics of CS
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