  But the most interesting exception is D1A1. In D1A1, Parmenides argues for D1A1C: that if the one is, then the one is not many. The reasoning is simple. From Oneness or Self-Predication, it follows that the one is one. Consequently, if the one is, then the one is one. But the property of being one and the property of being many are contraries, and, by Purity-F, no form can have contrary properties. Given that the one is a form, it follows that if the one is, then the one is not many. The non-obvious premises here are Oneness (or Self-Predication) and Purity-F. Whereas some might argue that D1A1 is unsound because Oneness (or Self-Predication) is false, others might argue that the very point of D1A1 is to show that if the one is and is many, then Purity-F is false.