This paper is a critical edition of Risalah fi Mafhum al-Mukhalafah written by Ahizade Abdulhalim Efendi, an Ottoman scholar from the 10th-11th (16th-17th) centuries. The section preceding the actual edition provides information regard- ing the author and his works as well as presenting an evaluation of the treatise. Mafhum al-mukhalafah (counterimplication), which is one of the key topics in usul al-fiqh (principles of jurisprudence), is approached by Ahizade in a differ- ent perspective. In his treatise, Ahizade examines the deductions (istidlal) made through mafhum al-mukhalafah in the works by Hanafi scholars on furu' al-fiqh (branches of jurisprudence), who are known not to accept mafhum al-mukhalafah as evidence. The treatise, which is the only work written on this topic, includes an introduction on the description and types of mafhum al-mukhalafah, a section on the cases in the Hanafite works where the authors appear to make deductions through mafhum al-mukhalafah and another section on cases where mafhum al- mukhalafah are unanimously considered as hujjah (proof)