This is both proven by intellectual reasoning and verified...

This is both proven by intellectual reasoning and verified by statements from the Book [kitāb] and Tradition [sunnah].[^1] Secondly, in view of the fact that religious statements in the Book and Tradition are general and limited, and that there are an unlimited number of actions and events that make up problematic areas, in order to realize the details of religious decrees there is no way but ratiocination [istidlāl]. It is clear to us that no other way has been shown in religious statements.

Here it becomes evident that in order to discern religious responsibilities, we must tread the path followed by intellectuals of the society in extracting personal and social responsibilities from general, specific, and normal commandments. Stated concisely, a series of specific rules must be utilized in order to deduce canonical duties and precepts from religious statements.

One who researches narrations of the Imāms will observe many cases where they engage in debate with sahābah, other followers, or their opposers whereby they deduce canonical precepts from the Book of Allah and Traditions of the Prophet (S) in the standard way. This is the meaning of ijtihād used in modern speech.

Therefore, ijtihād can be defined as gathering precepts of the sharī‘ah from religious statements through logical reasoning and a specific set of techniques—the formulae of religious jurisprudence. Hence, one of the duties Islam charges upon the Muslim society is scientific determination of religious precepts through ijtihād.

Clearly, not all Muslims are able to take up this duty and only a select number can become specialists and carry out this charge—obtainment of Islamic precepts through study of religious statements utilizing logical reasoning and rules of inference. The facts that not all people can employ ijtihād to discern precepts and that all people are obliged to learn religious precepts necessitate that Islam gives those who are not able to perform ijtihād another duty.

That is, they receive religious precepts required by their circumstances from individuals proficient in ijtihād and deduction. This is the meaning of the frequently used term taqlīd. The best reason justifying the precept of taqlīd regarding the uninformed is the ongoing practice among Muslims that has existed from the advent of Islam until today.