Abstract :
Hausman & Woodward present an argument for the Causal Markov Condition
(CMC) on the basis of a principle they dub ‘modularity’ ([1999, 2004]). I show that
the conclusion of their argument is not in fact the CMC but a substantially weaker
proposition. In addition, I show that their argument is invalid and trace this invalidity to
two features of modularity, namely, that it is stated in terms of pairwise independence
and ‘arrow-breaking’ interventions. Hausman & Woodward’s argument can be
rendered valid through a reformulation of modularity, but it is doubtful that the
argument so revised provides any substantially new insight regarding the basis of
the CMC.
