Reading guide

Newell, A. (1980) Physical Symbol Systems. Cognitive Science, 4, 135-183.

Allen Newell was a famous and influential computer scientist. He was one of the fathers of Artificial Intelligence. This paper was delivered at the first meeting of the Cognitive Science Society, which took place here at UCSD in 1979.

The paper by Newell is the most technical of the readings we will do this quarter. Do not get bogged down in technical detail. DO notice the overall structure of the paper.

The article presents the physical symbol system hypothesis (PSSH). This hypothesis states that wherever we find intelligence, including in the human mind, it will be an instance or example of a physical symbol system. The PSSH is presented as the solution to THE central problem in cognitive science: <<How can mind exist in the physical world?>>

Newell describes symbol systems, defines a simple example symbol system, and shows that this example symbol system is computationally equivalent to something called a Universal Machine.

A <<universal machine>> is not a physical machine. It is an abstract formal system that has a very important property; it can compute any input/output function that can be explicitly specified.

Universal machines and symbol systems can be made out of real material stuff in many ways. Every modern computer runs an operating system and programming languages that are examples of a physical symbol system.

The core of the paper is the Physical Symbol System Hypothesis (PSSH) stated on page 170. You should know the four parts of the PSSH.

The general characteristics of physical symbol systems on page 168 are essential.

The rest of the paper is there to give meaning to and to explain this hypothesis.

Vocabulary

Lisp: a programming language specifically constructed to support the manipulation of symbols. Most programming languages support arithmetic or mathematical operations. Lisp was created at Stanford in the 1960s and became the main language of early artificial intelligence.

Pushdown stack: an abstract computing device that serves as a memory into which things can be pushed one at a time, and from which things can be retrieved one at a time in the reverse of the order in which they were pushed into memory. Also known as last-in-first-out memory.

First order predicate calculus: a version of mathematical logic.

Use your dictionary to find the designation of these words:

Paradigmatic

Cybernetics

Legerdemain

Tautological

Milieu

Errata:

At the top of page 165, the bold font string <<in-then-else>> should read <<if-then-else>>.