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    ELECTRONIC NEWSLETTER ON  REASONING ABOUT ACTIONS AND CHANGE        
Issue 98018             Editor: Erik Sandewall             19.2.1998
Back issues available at http://www.ida.liu.se/ext/etai/actions/njl/
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                    *********  TODAY  *********

Today's newsletter contains the answer by Peter Grunwald to a
question to him in the Commonsense workshop discussions.


                 *********  DISCUSSIONS  *********

             ---  ARTICLES AT COMMONSENSE WORKSHOP  ---


        ========================================================
        |  AUTHOR: Peter Grunwald
        |  TITLE:  Ramifications and sufficient causes
        ========================================================

--------------------------------------------------------
|  FROM: Peter Grunwald
--------------------------------------------------------

> You mentioned in your talk that Lin's use of the mnemonic "causes" tends
> to be misleading. I agree with this, and indeed the observation from our 
> group to his work was that it was more or less a reformulation of what 
> had already been done using occlusion. However, I wonder if there isn't a
> similar problem with your use of the mnemonic "do". When you characterize 
> the Toss event using formulae such as Do(Heads(1),true), then who is it 
> that is doing something? 

Yes and no. `Yes' in the sense that the word `Do' may be misleading too
- - indeed, nobody needs to be doing something when a coin falls on the
table. `No' in the sense that I am very explicit in my article about the
`physics' of Do: I state precisely what has to happen in a domain in
order for $Do(X,B)$ to be the case in that domain; no such statement
about $Caused$ can be found in Lin's work. 

Namely, $Do(X,B)$ means that an intervention takes place that sets the
value of $X$ to $B$. A more appropiate term might indeed be $Set(X,B)$ or
$Intervention(X,B)$. I used $Do$ to stay close to Pearl's notation
(see J. Pearl, Causation, Action and Counterfactuals, TARK '96).

Lin's use of the predicate $caused$ has not such a clear interpretation.
It gets an implicit interpretation by the axioms it is involved in
(like $Caused(X,s,True) -> Holds(X,s)$) but it is not a priori clear what
has to be the case in the domain of interest in order for $Caused$ to be
true.

In other words, we do not really know what we are trying to model by the
predicate $Caused$ - that's the essential difference with $Do$.

Hope this is clear.

Peter

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