Letter to Science
What is Computer Science?
Science 1967 (157) 1373-4
Alan J. Perlis
Herbert A. Simon
Professors of computer science are often asked: “Is there such a thing as computer science, and if there is, what is it?” The questions have a simple answer:
Wherever there are phenomena, there can be a science to describe and explain those phenomena. Thus, the simplest (and correct) answer to “What is botany?” is, “Botany is the study of plants.” And zoology is the study of animals, astronomy the study of stars, and so on. Phenomena breed sciences.
There are computers. Ergo, computer science is the study of computers. The phenomena surrounding computers are varied, complex, rich. It remains only to answer the objections posed by many skeptics.
Objection 1. Only natural phenomena breed sciences, but computers are artificial, hence are whatever they are made to be, hence obey no invariable laws, hence cannot be described and explained.
Answer. 1. The objection is patently false, since computers and computer programs are being described and explained daily. 2. The objection would equally rule out of science large portions of organic chemistry (substitute “silicones” for “computers”), physics (substitute “superconductivity” for “computers”), and even zoology (substitute “hybrid corn” for “computers”). The objection would certainly rule out mathematics, but in any event its status as a natural science is idiosyncratic.
Objection 2. The term “computer” is not well defined, and its meaning will change with new developments, hence computer science does not have a well-defined subject matter.
Answer. The phenomena of all sciences change over time; the process of understanding assures that this will be the case. Astronomy did not originally include the study of interstellar gases; physics did not include radioactivity; psychology did not include the study of animal behavior. Mathematics was once defined as the “science of quantity.”
Objection 3. Computer science is the study of algorithms (or programs), not computers.
Answer. 1. Showing deeper insight than they are sometimes credited with, the founders of the chief professional organization for computer science named it the Association for Computing Machinery. 2. In the definition, “computers” means “living computers” - the hardware, their programs or algorithms, and all that goes with them. Computer science is the study of the phenomena surrounding computers. “Computers plus algorithms,” “living computers,” or simply “computers” all come to the same thing - the same phenomena.
Objection 4. Computers, like thermometers, are instruments, not phenomena. Instruments lead away to their user sciences; the behaviors of instruments are subsumed as special topics in other sciences (not always the user sciences - electron microscopy belongs to physics, not biology).
Answer. The computer is such a novel and complex instrument that its behavior is subsumed under no other science; its study does not lead away to user sciences, but to further study of computers. Hence, the computer is not just an instrument but a phenomenon as well, requiring description and explanation.
Objection 5. Computer science is a branch of electronics (or mathematics, psychology, and so forth).
Answer. To study computers, one may need to study some or all of these. Phenomena defines the focus of a science, not its boundaries. Many of the phenomena of computers are also phenomena of some other science. The existence of biochemistry denies neither the existence of biology nor of chemistry. But all of the phenomena of computers are not subsumed under any one exiting science.
Objection 6. Computers belong to engineering, not science.
Answer. They belong to both, like electricity (physics and electrical engineering) or plants (botany and agriculture). Time will tell what professional specialization is desirable between analysis and synthesis, and between the pure study of computers and their application.
Computer scientists will often join hands with colleagues from other disciplines in common endeavor. Mostly, computer scientists will study living computers with the same passion that others have studied plants, stars, glaciers, dyestuffs, and magnetism; and with the same confidence that intelligent, persistent curiosity will yield interesting and perhaps useful knowledge.