I'm reading my friend Dr. Gimbel's book on Einstein's Jewish Science, and in discussing Martin Luther's view of Christianity he quotes the following from Luther:
Therefore it is clear that, as the soul needs only the word of God for its life and Righteousness, so it is justified by faith alone and not any works; for if it could be justified by anything else, it would not need the Word, and consequently, it would not need faith.Gimbel takes that to mean, as is usual, that for Luther, Faith is sufficient for God's Grace. It is clear Luther means to entail that no works justify Grace. God's Grace, ("Life and Righteousness") do not come from anything you do, but from faith. But there is an argument presented here, and I'm not sure it does what Luther wants it to do.
First, lets take a look at the conclusion of the argument: The soul needs only the word of God for its life and righteousness. Let me use '->' to symbolize the material conditional. 'Only' reverses the order of the conditional, so as written, the claim is: R -> W, meaning that the word is a necessary condition for salvation, righteousness, Grace. If the soul only needs the word for salvation, the Word is a necessary condition. If you have life and righteousness, then you must have the Word, since it is only through the Word that you can have life and Righteousness.
It follows, according to Luther, that the soul is justified by faith alone, and not any works. He gives an argument. If it could be justified by anything else, it would not need the Word. This is straightforward: A -> ~W. And if it does not need the Word, it does not need Faith: ~W -> ~F. But it needs faith. F. Therefore, it does not need anything else. ~A.
So then we have the following premises:
A -> ~W
~W -> ~F
It certainly follows from that second argument
by Modus Tollens, and
By Modus Tollens as well. If you need Faith, nothing else is sufficient on its own. So you need the Word, and nothing else.
What does not follow is that Faith or the Word is sufficient for Grace. It only follows that nothing else is sufficient. For the Word to be sufficient, he would need
W -> R
to be entailed by the premises, but it is not. He has defended that Faith is necessary for Grace, but not that it is sufficient. Why couldn't it be that you have Faith, but still are not give Grace? Yet that is the conclusion he wants to draw: it is justified by faith alone. This simply does not follow from any premise given. "As the soul needs only the word of God for its life and Righteousness" does not entail "it is justified by faith alone and not any works."