Your last sentence really is the one that gets to the heart of the matter . I ' m not sure there is a physically definable essential difference . As Veritatis Splendor says In order to be able to grasp the object of an act which specifies that act morally , it is therefore necessary to place oneself in the perspective of the acting person and By the object of a given moral act , then , one cannot mean a process or an event of the merely physical order , to be assessed on the basis of its ability to bring about a given state of affairs in the outside world . Rather , that object is the proximate end of a deliberate decision which determines the act of willing on the part of the acting person . There may I don ' t know , I ' m not a doctor be cases in which someone has a valid medical reason to , say , touch a genital organ in a way that involves quick repetitive rubbing . What if that ' s the case for washing or rubbing on a lotion medicine or who knows and it causes an orgasm pretty consistently ? You might say well but that wasn ' t the intent , but isn ' t your whole position on moral objects that we can define and condemn some even independent of the question of intent ? But if the moral object in question can ' t be defined as rubbing the genitals until an orgasm results . then you ' re going to have to be a little more robust in explaining exactly how the moral object is defined and how it relates to the will as opposed to just a physical description of an event like that in the external world .