Cummins (1995) offers an analysis of causal and truth-functional suffi
ciency and necessity to predict and explain the effects on conditional
inferences of two pragmatic factors: alternative causes and disabling
conditions. However, the justification of these predictions is incons
istent. This note offers a modified analysis which puts her prediction
s on a sounder base: it is proposed that alternative causes and disabl
ing conditions affect judgments of argument validity under three diffe
rent models for the causal conditional.