These court categories were not, however, wholly exclusive: for instance, the Islamic courts—which were the Empire's primary courts—could also be used to settle a trade conflict or disputes between litigants of differing religions, and Jews and Christians often went to them to obtain a more forceful ruling on an issue. The Ottoman state tended not to interfere with non-Muslim religious law systems, despite legally having a voice to do so through local governors. The Islamic Sharia law system had been developed from a combination of the Qur'an; the Hadīth, or words of the prophet Muhammad; ijmā', or consensus of the members of the Muslim community; qiyas, a system of analogical reasoning from earlier precedents; and local customs. Both systems were taught at the Empire's law schools, which were in Istanbul and Bursa.