Laws are necessary regularities. Distinct from accidental generalisations. Deterministic and Indeterministic Laws. For deterministic laws only. Penicilin and recovery from illness.
R j is highly likely.
But this seems wrong. The I-S model can provide an explanation of an event on the basis of a set of true premises, and of its contrary on the basis of another set of true premises. And we can derive an explanation of R j and of not-R j . In order to resolve the problem of explanatory ambiguity Hempel proposed that the explanans of an I-S explanation should not be required to be true, merely accepted or believed. For otherwise it would seem that true I-S explanations can be given of both an event, or a phenomenon, and of its contrary.