 Fundamental or “original” nomological statements are those logically equivalent to a true sentence (with no terms that “essentially refer” to particulars) in prenex form with at least one universal quantifier and such that no logically stronger sentence in the same vocabulary is true. Derivative nomological statements are logical consequences of original nomological statements, but not all derivative nomological statements are “admissible.” To avoid conditionals true because of false antecedents (or sentences true because of irrelevant disjuncts), Reichenbach essentially requires that derivative nomological statements be the logically strongest sentences in their vocabulary that are consequences of original nomological statements. Statements are graded: Original nomological statements have grade 3, derivative nomological statements grade 2, and other statements grade 1. A counterfactual conditional can only be true—or assertible—if its antecedent has a grade at least as high as its consequent. Rather elaborate further conditions on logical form are imposed to avoid counterexamples. Counterfactuals about particulars are understood to be true if the corresponding indicative conditionals are instances of true nomological generalizations. 