I'm currently debating with someone whether something could be considered possible because we have no evidence that it's impossible. He made the statement that: "All things are possible which are not proven to be impossible", and attempted to justify it by claiming it's a truism (everything that is not ~A is A). I replied that his statement is not a truism because it doesn't have A/~A as his options, but A and "proven to be ~A".
He then offered me this:
"That objection doesn't seem to hold much merit given that the sentence structure indicates that two concepts are being included. First, you have the two clauses "A and ~A" then you have the contextual modifier "proven to be."
1) ∀X which are ~~ A -->A
2) ~W for ~A -->A
∀X ~W ~A ---> A
Are logically equivalent."
Since I'm new to logical notation, I'm having a hard time expressing the above arguments in normal language.
Can anyone help?