Pojman: subjectivism "makes morality a useless concept." (IP3 492a)

1. If subjectivism is is true, then "no argument about [moral matters] is possible" (IP3 492a).
2. If no argument about moral matters is possible, then morality is a useless concept.
3 Therefore, if subjectivism is true, then morality is a useless concept.(1, 2 HS)
4. Morality is not a useless concept.
5. Therefore, subjectivism is not true. (3,4, MT)