‘aql or reason which is endorsed by the Shari’ah and associated with jurisprudence, is different from the manipulative intellect which we use in our lives. Although the intellect is also endorsed by divine legislator, it is to be noted that the power of intellect is limited to perceptions and that it is unable to perceive the minute characteristics and details of something. Hence, man stands in need of another cognitive source that could help him understand the characteristics and details and that is ‘revelation’. In Islam, the divine revelation becomes manifest through one of the following two things:
1. The Quran and Sunnah: In addition to the meaning of the Quran, the words of the Quran have also been revealed. It is wrong to believe or say that only the meanings of the Quranic verses, as some believe, are part of the revelation. In Islamic culture, the distinction between Hadith Qudsi (Sacred Hadith) and the Quranic verses is that Hadith Qudsi is the word of God repeated by Muhammad and recorded on the condition of an isnad. As for the Quran, both its words as well as it meanings are revealed and sent down by God upon the heart of the Prophet (pbuh).
2. Another manifestation of the revelation is the narrations (revayat) in the sense that the Prophet (pbuh) does not speak of his own whims and desires as the Quran says: “He does not speak of his own desire. It is only revelation which is revealed to him.” 
Also, it has also been reported that one of the narrators who was upset came over to the Prophet (pbuh). The Prophet (pbuh) asked: “Why are you upset?”
He said: “I write whatever you say but Quraish forbade me from doing so saying: ‘Why are you writing what the Prophet says? The Prophet is also a human being. He says something when he is angry and another thing when he is happy.’”
The Prophet (pbuh) said: “Write [what I say]. By Allah, in Whose hand is my soul, I never utter anything except the truth.  ”
The Ahlul-Bayt (a.s.) are those who know the interpretation of the Quran which says, “none knows its interpretation except Allah, and those who are firmly rooted in knowledge.”  Only the infallible Imams (a.s) are deeply rooted in knowledge and they are the ones who know how to interpret the Quran because they are acquainted the origin of the Quran, albeit through divine knowledge.
Given the foregoing explanation, if we want to know a special feature in a religious issue, we must turn to the Quran and hadith but we should also keep in mind that in order for us to understand the Quran, we need to know Arabic literature, the concepts and culture of the time of revelation and also the narrations because the narrations interpret the verses and some of them restrict and qualify the verses. Knowing the narrations also require us to know the various chains of transmissions of narrations. It is necessary to deal with every narration and make sure whether its chain of transmission is valid and reliable or not. Such inquiries need methodological discussions that are raised in legal theories. The entirety of this information is something which is described as “Ijtihad”. Thus, it is a specialization with which a person can refer to Islamic sources (i.e. the Book of God and the Sunnah of the Prophet and also reason) to discover and deduce Islamic laws.
Indeed, the intellect has a limited capacity and a Mujtahid (practitioner of Ijtihad) deduces most of the Islamic laws through the fundamentals and words of the Book and the Sunnah. There is no doubt that all people are not and cannot be Mujtahids because Ijtihad is a competence which is not easily achievable. One has to make a great deal of efforts to become competent enough to deduce legal laws. The Quran also states that it is not necessary for all to specialize in religion; rather a group of people must engage in studying and understanding the religion  and the Mujtahid should be a person from amongst them.
The Place of Reason in Deducing Shari’ah Law
Taqlid has two meanings: 1) A negative meaning which in Persian language implies following someone blindly, a meaning which is generally despised by the public. Balkhi Rumi says in his famous poem as such:
Khalq ra taqlid shan bar baad daad
Ay doosad la’nat bar ein taqlid baad. 
[The people were destroyed owing to their blind imitation. May a thousand curses be upon such an imitation.]
This poem refers to the negative imitation i.e. a blind and reasonless emulation. When something becomes a fashion and others follow without knowing the reason, it is an imitation which brings about the misery of the people.
2) Another meaning of Taqlid is associated with Islamic jurisprudence which means referring to and seeking the advice of an expert in a technical matter. Hence, unlike the first meaning which is unwanted and rejected, the second meaning of “Taqlid” is completely acceptable and rational. The most important reason for the permissibility of Taqlid in religious affairs rests in the very rational point that every layman or inexpert individual turns to an expert for advice on technical and specialized issues. For example, when a person becomes ill, he visits a doctor simply because the doctor specializes in this field. Hence, since all people cannot specialize in jurisprudence, it is necessary upon them to refer to a Mujtahid and an expert in religious affairs. This is quite rational as it signifies the positive meaning of Taqlid.
Read the follow articles to learn more about Taqlid:
1. Reason and the Extent of Its Activity, 1110 (site: 1888).
2. The Manipulative Intellect, Mind, Faith and Love 839 (stie:909)
3. Faith and Reason, 4910 (site: 5284)
4. The Philosophy of Taqlid and the Unexplained Proofs, 2441 (site:2991)
5. Acting upon One’s Own Research Rather than Following a Mujtahid, 9180 (site: 9179)
6. The Reasons behind the Necessity of Following Jurists (Maraje’) 975 (site: 1078).
7. Denunciation of Taqlid, 8165 (site: 8320).
 – Al-Najm: 3-4 «وَ ما یَنْطِقُ عَنِ الْهَوى، إِنْ هُوَ إِلاَّ وَحْیٌ یُوحى»
 – Ahmad bin Hanbal, Al-Musnad, vol.2, pg.162, quoted by Subhani, Ja’far, “Encyclopedia of Jurists’ Categories”, vol.1, pg.179; Tantavi, Sayyid Muhammad, al-Tafsir al-Wasit Lil-Quran al-Karim, vol.14, pg.59.
 – Aal-e Imran: 7 – وَ ما یَعْلَمُ تَأْویلَهُ إِلاَّ اللَّهُ وَ الرَّاسِخُونَ فِی الْعِلْم
 – Al-Tawbah: 122.
 – Balkhi, Mawlana Jaluddin Muhammad, Mathnawi Ma’navi (Spiritual Couplets), second copy, pg.204, Bulaq Publication, 1835.