Communications of the ACM

core theory. In several papers, Joseph Y. Halpern and Judea Pearl have developed the concept of causality in artificial intelligence, but their motivations and examples suggest application to “early stage” research, just as Bertrand Russell wrote.

I submitted this letter mainly to prompt thinking on what role the causality concept should play in the progress of various areas of computer science. Today, it is used in computer systems, software engineering, and artificial intelligence, among others, probably. Should we thus aim for its progressive elimination, leaving it a role only in the area of explanations and early-stage intuitions?

Luigi Logrippo, Ottawa-Gatineau, Canada

Communications welcomes your opinion. To submit a Letter to the Editor, please limit yourself to 500 words or less, and send to letters@cacm.acm.org.

end, I will be sharing the article with fellow leaders in my organization and recommend you share it with yours as well.

Geoffrey A. Lowney, Issaquah, WA

Professionalize CS Education Now

Computer science as a discipline has been remarkably bad at marketing itself. With current record enrollments in American universities, this is not a problem, but consider how it might play out in an uncertain future. People today using computers, cellphones, tablets, and automated highway toll payment devices, as well as multiple websites and services on a daily basis lack a clear idea what computer scientists actually do, and that they are indeed professionals, like lawyers, accountants, and medical doctors.

Parents concerned about the earning potential of their children and of their children’s future spouses forever try to address the conundrum of what academic path to take, as in, say, medical school, law school, or business school.

I thus propose a simple semantic change, and the far-reaching organizational change it implies. Master’s programs in computer science shall henceforth graduate “computists” and rebrand themselves as “ computing schools.” Future parents and par-ents-in-law should be able to choose among, say, medical school, computing school, business school, and law school. Existing Master’s curricula in computer science would be extended to five or six semesters, with mandatory courses in all areas of applied computing, from the perspectives of building systems and selecting, evaluating, adapting, and applying existing systems in all facets of computing, based on scientific methods and precise metrics.

When this basic framework is established, computing schools would stop accepting the Graduate Records Exam ( http://www.ets.org/gre) and switch to their own dedicated entrance exam, in the same way the LSAT is used for law school and the MCAT for medical school. The conferred degree would be called, say, Professional Master of Computing.

It might take a decade or more to
change the perception of the Ameri-
can public, but such change is es-
sential and should be embraced as
quickly as possible and on a national
basis. ACM is best positioned and able
to provide the leadership needed to
move this important step forward for
the overall discipline of computer sci-
ence.

James Geller, Newark, NJ

Causality in Computer Science

I would like to congratulate Carlos Baquero and Nuno Preguiça for their clear writing and the good examples they included in their article “Why Logical Clocks Are Easy” (Apr. 2016), especially on a subject that is not easily explained. I should say the subject of the article is quite far from my usual area of research, which is, today, formal methods in security. Still, we should reflect on Baquero’s and Preguiça’s extensive use of the concept of “causality.” That concept has been used in science since ancient Greece, where it was developed by the atomists, then further, to a great extent, by Aristotle, through whose writings it reached the modern world.

The concept of causality was criticized by David Hume in the 18th century. Commenting on Hume, Bertrand Russell (in his 1945 book A History of Western Philosophy) said, “It appears that simple rules of the form ‘A causes B’ are never to be admitted in science, except as crude suggestions in early stages.” Much of modern science is built on powerful equations from which many causal relationships can be derived, the implication being the latter are only explanations or illustrations for the relationships expressed by the former.

Causal laws are not used in several well-developed areas of computer science, notably complexity theory and formal semantics. In them, researchers write equations or other mathematical or logical expressions. At one point in their article, Baquero and Preguiça redefined causality in terms of set inclusion. Leslie Lamport’s classic 1978 paper “Time Clocks, and the Ordering of Events in a Distributed System” (cited by Baquero and Preguiça) seems to use the concept of causality for explanations, rather than for the

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