Several revisions of the Hempel and Oppenheim definition of explanation have been offered in recent years, and none have gone uncriticized in the literature. In the present paper it is argued that the difficulties involved with these attempts are based upon a confusion between three types of explanation, and that Professor David Kaplan's model of S-explanation provides a uniform treatment of all three types.

In, it was argued that Professor David Kaplan's model of S-explanation could be formulated so as to provide a unified framework for three types of explanation, viz., potential, rationally acceptable, and true. In this note I correct an error in the statement of the conditions for a potential direct S-explanans, show that the corrected version leads to a further simplification in the conditions of the model, and propose a fourth type of explanation which the framework of S-explanation can accommodate.