Ebû Bekr er-Râzî el-Cessâs's istihsan approach and fürû fikha application

The basis of Islamic law is the Qur'an and the Prophet. It is the sunnah of the Prophet (sav). These two main sources are content with determining the main rules and procedures that help to organize the legal life. Judgment of the issues that are not included in these sources has been determined by the jurisprudence from these two sources. Although the ijtihad activities were mostly carried out on the determination of the indication of the word or the activity of comparison, sometimes these methods could not answer the new issues. In this context, Islamic jurists searched for new ijtihad methods. As a result of these searches, the Hanafi sect, in cases where the established rule has reached a dead end or the principle of equity has lost its functionality; They discovered the method of istihsan, which can be defined as "shar'i evidence, which expresses the method of finding a solution in accordance with the spirit of the event by separating from the open qiyas, general and established rule for special reasons". The fact that the istihsan method is not defined by the first users; It has caused serious discussion in the history of Islamic law. Later Hanafi scholars made great efforts to defend istihsan. In this sense, it is a fact that the works of Cessâs, one of the Hanafi scholars, should be examined. Key Words: Ijtihat, Usûl, Furû, Qıyas, al-'Illah, Takhsıs, al-Jassas, Istıhsan.