Qiyas Islamic Jurisprudence
This answer must not go against above mentioned sources and should be related to them.
Qiyas islamic jurisprudence. And the ijma is what ulama understood from quran and hadees. The essential requirement of qiyas are asl original case on which a ruling has been given hukm ruling on the original illah cause of ruling in the original case and far new case on which ruling is to be given. According to this method the ruling of the quran or sunnah may be extended to a new problem provided that. So ijma and qiyas both are important for understand islamic shareeah and quranic rules.
Qiyas in islamic law the deduction of legal prescriptions from the quran or sunnah by analogic reasoning. Qiyas and ijma both are considered as base of understanding islamic laws after quran and hadees. If answer is not found in any of the sources mentioned above then qiyas is done. There can be difference of opinion on the law derived through qiyas as is the case with almost all ijtihadi law.
Qiyas is using your own mind to find an answer of a question. The qiyas is actually a way to understand a rule from quran and hadees. Qiyas provided classical muslim jurists with a method of deducing laws on matters not explicitly covered by the quran or sunnah without relying on unsystematic opinion ray or hawa. With the qurʾān the sunnah and ijmāʿ scholarly consensus it constitutes the four sources of islamic jurisprudence uṣūl al fiqh.