Our current mortgage system provides an excellent example of why usury used to be illegal. Many people today believe that usury is just another word for interest, but that is not strictly correct. George O'Brien gives a more thorough explanation of usury in "An Essay on Medieval Economic Teaching," but one aspect of usury is the attempt to conduct a transaction without any risk, or where the risk is only one-sided. One of the fundamental differences between Capitalism and Distributism is the attitude toward usury.