In Confessions, book 7 chapter XII, St. Augustine writes:
- If things are sovereignly good, they are incorruptable.
- If thing is corruptable, it contains good.
- Evil is either an incorruptible substance or a corruptible substance.
- If evil in incorruptable, it's soveregnly good.
- If evil is corruptable, it contains good.
To my mind, in derivations 4 and 5 Augustine perceives implication in reverse order.That violates the laws of logic. Am I right?
a) A → ¬B (if sovereignly good, they were incorruptible)
b) supposing ¬B, therefore ¬B → A (for either it should be an incorruptible substance, and so a chief good)
Here is a logical mistake, like : A → ¬B (if color is black, it's not green) ; ¬B → A (color is not green, therefore, it's black)