The furu' concern the traditions which elaborate the details of religious law...

The furu' concern the traditions which elaborate the details of religious law, while the rawda is a collection of traditions outlining various points of religious interest and including some of the letters and speeches of the Imams. One of the principal features of the work is that the traditions are presented systematically in chapters according to their subject matter.

This is a system which Islamic scholars had begun to use in the second half of the second century and in the third century of the Islamic era. Al-Kulaini was not the first Imami scholar to use the method. There are other works of traditions which use the same method, notably Kitab al-Mahasin of Ahmad b. Muhammad b. Khalid al-Barqi (d. 274/887).[^4] However it seems to have been the first work to present such a comprehensive survey of Imami traditions in this manner.

The source collections of traditions were known as usul. These were collections of traditions, either heard directly from the Imam or at least at second hand.

There were said to have been four hundred of such collections.[^5] These traditions were not arranged in chapters according to subject but arranged in the order in which the traditions were heard, regardless of subject matter or which particular Imam they were heard from.[^6] It was these usul as well as earlier edited collections which were the basis of al-Kulaini's collection as he heard them taught by earlier scholars.

Unfortunately with the development of the comprehensive collections, the usul must have become less important, and only a few survive in manuscript. Traditionists before al-Kulaini and traditionists after him, examined the isnads (chain of authorities) with great care. Their purpose was to make sure that all reporters of a particular tradition were men of true faith; al-Kulaini himself seems to be less concerned with the isnad than with the matn or content of the tradition.

Thus he sometimes reports traditions with men in the isnad, who were not strictly speaking disciples of the Imams; sometimes they belong to a different persuasion like the Zaidis, sometimes they are ghulat, extremists in their views.

Some men in the isnads are those who regarded one of the earlier Imams as the final Imam and there are even men entirely unconnected with Shi'i views.[^7] The scholars of tradition elaborated a system of categorising the different traditions according to the level of authenticity of a tradition, in terms of isnad and subject matter.