Interest or usurious interest. Quranic verses prohibit riba, a practice that doubled a debt if the borrower defaulted and redoubled it if the borrower defaulted again. Islamic legal scholars have historically interpreted this as prohibiting any loan contract that specifies a fixed return to the lender, since it provides unearned profit to the lender and imposes an unfair obligation on the borrower. In the modern world, most Muslim countries allow the charging of moderate interest, prohibiting only usurious or compound interest, although some reformers condemn all interest as an impediment to social justice. Prohibition of interest is considered by them as critical to Islamic economic reform.