The Sunnis said that the valid proofs were four in number...

The Sunnis said that the valid proofs were four in number: the Book, the Sunna, ijma and ijtihad (qiyas); the Shi`a said the valid proofs were four: the Book, the Sunna, ijma` and `aql (reason). They merely substituted `aql for qiyas. At any rate, 'ijtihad' gradually found a wider meaning, i.e., the employment of careful consideration and reasoning in reaching an understanding of the valid proofs of the shari`a.

This, of course needs a series of sciences as a suitable preliminary basis on which to develop the ability to consider and reason correctly and systematically.

The `ulama of Islam gradually realized that the deduction and derivation of the precepts from the combined valid proofs of the shari`a necessitated [the learning] of a series of preparatory sciences and studies such as the sciences of literature, logic, the Qur'anic sciences and tafsir (Qur'anic exegesis), the science of hadith and the narrators of hadith (rijal al­hadith), the science of the methodology of usul al­fiqh, and even a knowledge of the fiqh of the other sects of Islam.

A mujtahid was someone who was a master of all these sciences. I think it extremely likely, though I cannot state this categorically, that the first person among the Shi`a to use the words ijtihad and mujtahid [positively] was the `Allama al­Hilli.[^18] In his work " Tahdhib al­usul'', he puts the chapter on ijtihad after the chapter on qiyas, and there he uses the word in the same sense in which it is used today.

[We can therefore say that] the ijtihad which is forbidden and rejected in the eyes of the Shi`a is ra' y and qiyas, which were originally called ijtihad, whether this is counted as a source of the shari`a and as an independent basis for legislation, or taken as a means for deriving and deducing true precepts; whereas the ijtihad which they deem correct according to the shari`a is that which means effort and exertion based on expert technical knowledge.

In answer to the question: what is the meaning, the use and the place of ijtihad in Islam, it can thus be said that it is ijtihad in the meaning that it is used today, i.e., competence and expert technical knowledge.