Given that I can't infer an 'ought' from an 'is', am I always to assume then that moral arguments which seem to make this move actually have an implicit moral assumption? For example: 1. If you did that, you'd be hurting your sister unnecessarily. 2. (unstated) unnecessarily hurting your sister is wrong. 3. (unstated) you shouldn't do what's wrong. So you shouldn't do it.