The only time the Shi'ah met with any difficulty in this...
The only time the Shi'ah met with any difficulty in this regard with the beginning of the Minor Occultation of the Twelfth Imam (A), a period of 69 years from 260/874 to 328/940. During this period the Shi'ah could obtain replies to their queries through the deputies (nuwwab) of the hidden Imam (A) who served as intermediaries. These deputies, one after another, were four: Abu `Amr `Uthman ibn Sa`id, Abu Ja'far Muhammad ibn `Uthman (d.
304 or 5/916 or 7), Abu al-Qasim Husayn ibn Ruh al-Nawbakhti (d. 326/938), and Abu al-Hasan `Ali ibn Muhammad al-Samari (d. 329/941).
With the end of the Minor Occultation and the beginning of the Major Occultation in the year 329/941, in the absence of access to the Imam (A) or his deputies, the Shi'ah were confronted with greater difficulty in regard to obtaining ahkam for new issues, which increased with the passage of time and the growing distance from the era of nass, together with the growing variety of the emergent issues and problems created by new conditions of life.
Moreover, with the passage of time, increasing number of doubts took the place of the previous certainty about the meaning and import of the texts which served as the bases of legal deductions. It was at this time that the Shi'ah began to search for ways to solve this problem by deducing the ahkam for new issues from the available legal sources. This new path was that of "ijtihad " whose pioneer was the treat mujtahid and creative jurisprudent al-Hasan ibn Abi `Aqil al Umani.