OK Christians. your chance. Convince me of God.

[The Grand Nudger]

Agreed, the argument I offered is invalid, but in what way does it differ from your own?

Ok the first argument I worded it like this.

Not A -> B
Not B
Therefore A.

Then I think you got confused with double negation,

So I re-wrote as

A -> B
Not B
Therefore Not A

Both of these are logically valid.

From other then God. The negation of that is "from God". The negation of "from God" is from "other then God".

Yours was written like this.

A -> B
B
Therefore A.

Which is invalid.

My confusion doesn't arise from negation or either of the two forms you are hoping to use in this argument Mystic (which is why I linked the wiki's I've been referring to...I do get things wrong often enough, you know, I try to check my own work..lol) My confusion arises in whether we're arguing that B is a necessary or a sufficient condition of A (and vice versa). Seeing as you applied the "if/then" and not "if and only if/then" - in addition to your later comments were looking at modus ponens, a valid form being

If A, then B
A
Therefore B

but not modus tollens, a valid form being

If A, then B
Not B
Therefore not A

These are the two arguments you are putting forward, correct? Am I mistaken in this, can you use modus tollens if the converse of the premise is not valid? If you're arguing sufficient condition (but not necessary condition) then the rule of inference (MP) set next to your own looks like this

Mystic-If A, then B
MP -If A, then B

So far so good.

Mystic-Not B
MP -A

Wtf just happened? The MP essentially states, If this statement is true(A), then it implies such and such (B) (that would be the line above), and then goes on the assert that the statement (A) is true. You're making some assertion about B at this point, why?

Mystic-Therefore Not A
MP- Therefore B

Ummm........again, MP seems to be drawing some conclusion about B, while you are drawing some conclusion about A

You seem to be attempting to use the rules of inference for neccesary condition in an argument (presumably) from sufficient condition. To leverage the MT wouldn't you be asserting necessary condition?

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Ah, something I missed earlier, when you were explaining that you felt that b could be true even if a were not, but that a could not be true if b were not. Can't say I agree with you on that count, and that's part of establishing necessary condition.