 Salmon was ingenious in devising “screening off” criteria to insure that the properties cited in an S-R explanation were restricted to those that were statistically relevant. He may have appreciated that the available evidence was restricted to relative frequencies in finite sequences, but that could be discounted as typical of the distinction between a context \(\mathbf{K}\) representing our total knowledge at that time and the truth condition, since scientific knowledge is always tentative and fallible. A deeper problem arose from the existence of properties that were statistically relevant but not explanatorily relevant, however. If women whose middle initials began with vowels, for example, experienced miscarriages with a different frequency than women whose middle initials began with consonants—even after other properties were taken into account—then that property would have to qualify as statistically relevant and therefore explanatorily relevant (Fetzer 1974, 1981). This result implied that statistical relevance cannot adequately define explanatory relevance, and Salmon would gradually move toward the propensity approach in Salmon (1980, 1989).