You should probably study it further, as it's unclear as to whether you adequately understand it or not (no offense, sincerely).
You have to realize that "negation" and "opposite" are not the same thing. This is a typical error made by beginning students of logic.
For instance, the negation of "all" is not "none", it is "not all", or "some".
The negation of "all" is "some", not "none".
And the denial of "sin nature" is NOT "sinless nature".
Ironically, I was going to share Augustine's argument with you earlier, as it seems to go against your own position.
For the benefit of the lurkers:
Pre-fall | posse peccare,
posse non peccare | able to sin,
able to not sin |
Post-fall unregenerate | non posse non peccare | not able to not sin |
Post-fall regenerate | posse non peccare | able to not sin |
glorified man | non posse peccare | unable to sin |