Ijtihad
Definition:
Linguistically, ijtihad means exerting strenuous effort to attain something difficult.
Technically, it is the exertion of effort to arrive at a legal ruling.
A mujtahid is the one who undertakes that effort.

Conditions for ijtihad:
Ijtihad is subject to several conditions, among them:
1 – He must know the relevant scriptural proofs needed for his reasoning, such as the Qur’anic verses of rulings and the related hadiths.
2 – He must be able to assess the authenticity or weakness of a hadith, including familiarity with its chain of transmission, the narrators, and similar matters.
3 – He must know the abrogating and abrogated texts and the points of scholarly consensus, so that he does not base a judgment on evidence that has been abrogated or that contravenes consensus.
4 – He must recognize the qualifiers within the evidence—such as specification, restriction, and the like—that alter a ruling, so that he does not issue a judgment at odds with them.
5 – He must have sufficient knowledge of Arabic and of the principles of jurisprudence (usul al-fiqh) that pertain to the meanings conveyed by words—such as the general and the specific, the absolute and the qualified, the ambiguous and the clarified, and so forth—so that he rules in accordance with those semantic indicators.