Dr. Pearl,
I am at the halfway of your book Causality, which I think to be
excellent and instructive. What I am writing to you is that
I browsed to homepage of Dr. Lotfi Zadeh and found out that he has
a Word document whose subject is 'CAUSALITY IS UNDEFINABLE'. The page is
http://www.cs.berkeley.edu/~nikraves/zadeh/Zadeh2.doc.
I know you have answered many times reports like that, so if there
is already discussion going on of this subject I would appreciate
the URL/name of the journal as I am really interested
in the subject.
Author's Reply:
Dear Sampsa,
Thanks for writing to me.
I am puzzled by
Zadeh's claim that 'CAUSALITY IS UNDEFINABLE'.
For me, the adequacy of a definition lies not in abstract
argumentation but in whether the definition leads to useful
ways of solving concrete problems. The definitions of causal
concepts that I have used in my book
have led to useful ways of doing things, and to
meaningful assessments of the risks associated with doing
things one way or another (e.g., choosing treatments, or
adjusting for confounders). If Zadeh were to present us with
alternative definitions or with alternative ways of solving
causality-related problems, we would be able to
judge their merits. But until this happens, claims of
"undefinability" leave me mildly puzzled, somewhat amused,
but scientifically unmoved -- there are urgent problems
out there awaiting solution.