We look more carefully at the modeling of causality using structural
equations. It is clear that the structural equations can have a major impact on
the conclusions we draw about causality. In particular, the choice of variables
and their values can also have a significant impact on causality. These choices
are, to some extent, subjective. We consider what counts as an appropriate
choice. More generally, we consider what makes a model an appropriate model,
especially if we want to take defaults into account, as was argued is necessary
in recent work.Comment: In Heuristics, Probability and Causality: A Tribute to Judea
Pearl (editors, R. Dechter, H. Geffner, and J. Y. Halpern), College
Publications, 2010, pp. 383-40
