 Moreover, Salmon disagreed with Carnap’s justification of induction in terms of inductive intuition (Carnap 1968). Salmon held the frequency interpretation to come closest to satisfying all of the adequacy requirements, although it faced serious difficulties with ascertainability, especially in connection with single case probability attributions. However, Salmon deemed the solution promising in terms of weight referred to homogeneous reference classes  (§ 2.1).  In addition, he regarded the frequency theory as the only interpretation offering a viable approach to the justification of induction.