Friday, 16 September 2011
Screening-off and Causal Incompleteness
Elliott Sober (coauthored with Mike Steel)
University of Wisconsin-Madison
3:30 pm, 817R Cathedral of Learning

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Abstract: We begin by considering two principles, each having the form causal completeness ergo screening-off.  The first concerns an intermediate link in a causal chain; the second describes a common cause of two or more effects. They are logically independent of each other and each is independent of Reichenbach's principle of the common cause.  Simple examples show that causal incompleteness means that screening-off may fail to obtain. We derive a stronger result: in a rather general setting, if the composite cause C₁& C₂&...& C_n screens-off one event from another, then each of the n component causes C₁, C₂, ..., C_n must fail to screen-off. The idea that a cause may be ordinally invariant in its impact on different effects is defined; it plays an important role in establishing this no-go theorem. We argue that this theorem is relevant to assessing the plausibility of the two screening-off principles.