Luther on Reason

In reading Roland Bainton's book on Luther, Bainton points out that when Luther assaults reason, he is assaulting common sense, not scientific deduction. At seminary, much ink was spilled over the Wesleyan quadrilateral, with people often assailing reason or staunchly defending it. Maybe we are dealing with a Lutheran problem in reason - people mean different things by the word reason.
Luther also talks about usury. His idea for debt really speaks to today's subprime situation. Luther wants borrower and lender to share the risk of loss on the loan (seemingly asking lenders to be cosigners to loans). That is an interesting concept. Lenders who shared in economic loss would be more cautious.