Ilm al Khilaf a science which deals with the Islamically sound arguments used by Muslim jurists (fuqaha) to reach their various legal opinions. As such, it can also be known as comparative Islamic law. Historically, the various madhahib of Islam shared and benefitted from this science, and there is no reason why we also cannot benefit from it.
We know that there were differences of opinion and practice even during the time of the Prophet Muhammad, for his Companions did not view everything the same way. This state of affairs naturally continued after the Prophet’s death. The suhuf ascribed to some of the Companions and the information given in the relevant biographical literature were studied for details. The fiqh-related issues debated by the Companions increased in number and complexity during the time of the Successors (Tabi’un),w hen the development of Islamic jurisprudence was just getting started.