As usual, Kathy's comments on hidden events,
counterfactuals and causality have hit the target. What I should like to
do is add a few points to what she said.
Causality is one of the most basic concepts in human
cognition. Perceptions of causality play a pivotal role in decision
making. Causality has been an object of discussion and debate since the
times of Aristotle and, more recently, Hume. Countless attempts to
formalize causality have been made, but to no avail.
The problem is that causality is not a bivalent concept�as
it is commonly assumed to be in attempts at formalization. Causality is
a matter of degree. Here are a few simple examples which illustrate the
point.
I am a manufacturer of raincoats. To increase sales, I
increased the advertising budget by 20%. Sales went up by 10%. Was the
increase in sales caused by the increase in advertising? If so, to what
degree? The question cannot be answered because the increase in sales is
the top of an iceberg. Other events -some visible and some not- which may
have played a role were rainy weather, bankruptcy of a competitor,
improved styling, and so on ad infinitum. In this setting, how can a
degree of causality be associated with the designated events: (a)
increase in the advertising budget; and (b) increase in sales. There is
no theory which can answer this question.
The same problem arises in identifying the cause of death in
a death certificate. It has to be done by law, but every doctor knows
that what is done is a very crude approximation to a complex reality.
Causality can be treated�and has been treated rigorously�in
physics, system theory and related fields. But in human�centered
systems, this is not the case. In fact, in the realm of such systems it
is hard to find instances in which an assertion of causality is beyond
question. Example: George shot and killed John. Did George cause John�s
death? At first glance, it appears that the answer is �yes.� But suppose
that George was hired by Tom to kill John. Given this information, to
what degree, if any, did Tom cause John�s death. Questions like this
pervade legal reasoning, but there is no theory to resolve them.
In summation, there does not exist a formalized theory of
causality which is capable of dealing with questions such as those posed
above. But what is more unsettling is that it is hard to see how an
operational theory of causality could be developed. Lowering our sights,
what may be possible is to construct a theory of causality in which
ordering of causes is ordinal, partial and conditioned on available
information.
Lotfi
P.S. A point which should be clarified is that my comments and examples
are not directed at assertions about cumulative causality exemplified by
"heavy smoking causes lung cancer", and "overeating causes obesity."
Such assertions raise issues which go beyond those that are touched upon
in my comments.
--
Lotfi A. Zadeh
Professor in the Graduate School, Computer Science Division
Department of Electrical Engineering and Computer Sciences
University of California
Berkeley, CA 94720 -1776
Director, Berkeley Initiative in Soft Computing (BISC)
