The hadith literature can broadly be divided into at least four categories depending on the themes dealt with in traditions.

Firstly, there is the part which is concerned with matters of doctrinal significance (usul al-Din).

Secondly, there are traditions which deal with spiritual and ethical themes (Irfan and akhlaq).

Thirdly, there is the great mass of traditions concerned with law and legal issues (fiqh).

Fourthly, there are the traditions which deal mainly with history and historical incidents.

Of the four major collections of Shi`i hadith, namely al-Kafi, al Tahdhib, al-'Istibsar, and Man layahduruhu al-faqih, only a part of al-Kafi deals with doctrinal and ethical themes. The rest of al-Kafi as well as the whole of the three other collections, deal mainly with legal matters. This part ofal-Kafi dealing with doctrinal, ethical and historical themes consists of the books constituting Usul al-Kafi and Rawdat al Kafi.

Usul al-Kafi is the first part of al-Kulayni's al-Kafi that deals with themes of doctrinal and ethical significance in a systematic manner. Rawdat al-Kafi, which deals with miscellaneous themes, is a record mostly of the sermons, letters, polemics, episodes, etc. of the Prophet (S) and the Imams (A). Usul al-Kafi contains eight books in the following order:

(1) Kitab al-`aql wa al jahl (The Book of Intellect and Ignorance, contains 34 traditions),

(2) Kitab fadl al-ilm (The Book of the Merits of Knowledge, contains 176 traditions),

(3) Kitab al-tawhid (The Book of Divine Unity, contains 212 traditions,

(4) Kitab al-hujjah (The Book of God's Proofs, contains 1015 traditions),

(5) Kitab al- iman wa al-kufr (The Book of Belief and Unbelief, contains 1609 traditions),

(6)Kitab al-du'a' (The Book of Invocation, contains 409 traditions),

(7) Kitab `azamat al-Qur'an (The Book of the Greatness of the Quran, contains 124 traditions), and

(8) Kitab al-mu`asharah (The Book of Social Ethics, contains 464 traditions).

Thus the eight books of Usul al-Kafi, which consists of two volumes, contain 3783 traditions. The entire al-Kafi is said to contain 16,199 traditions, including 11,156 traditions of the Furu` al-Kafi. Not all traditions of al-Kafi are of equal reliability. According to the great Imami scholar Zayn al-Din al-`Amili, known as al-Shahid al-Thani (911-966/1505-1559), who examined the asnad or the chains of transmission of al-Kafi'straditions, it consists of 5072 sahih, 144 hasan, 1118 muwaththaq, 302 qawi and 9485 traditions which are categorized as daif.

Traditions fall into two basic categories: mutawatir and ahad. A hadith is said to be mutawatirwhen it, has been narrated by so many different chains of narrators belonging to various periods and different regions of the Islamic world, and in so many different wordings as to preclude any doubt about its authenticity. Traditions which are not mutawatir are termed as ahad or wahid.

The ahad traditions in turn are classified into various categories by Shi`i scholars, according to the qualities of their asnad and the repute of narrators in a chain. These categories, in a decreasing order of reliability are: sahih, hasan, muwaththaq and da'if. A sahih tradition is one which is free from any kind of defect in its unbroken chain of transmission and is narrated by transmitters of well-known veracity (thiqah).

This selection from Usul al-Kafi is based on the selection published by Muhammad Baqir Mahmudi, in Arabic under the title Sahih al-Kafi and with Persian translation with the title Guzideh-ye Kafi (vol.1, Markaze Intisharat-e `Ilmi wa -Farhangi: Tehran, 1363 H. Sh) All the ahadith selected here fall, according to his estimation, in the category of sahih traditions from the viewpoint of asnad.

The main sources of information about the reliability of Shi`i narrators are:

1. Fihrist asma' musannifi al-Shi'ah, known as Rijal al-Najashi, by Abu al-`Abbas Ahmad ibn `Ali ibn Ahmad ibn al-`Abbas al-Najashi al Asadi al-Kufi (372-450/982-1058), referred to in the notes as N.

2. Rijal al-Tusi, By Shaykh al-Ta'ifah Abu Ja'far Muhammad ibn al Hasan al-Tusi (385-460/995-1067), referred to in the notes as Tr.

3. Fihrist al-Tusi, also by Shaykh al-Ta'ifah al-Tusi, referred to here as Tf.

4. Ikhtiyar ma`rifat al-rijal, known as Rijal al-Kashshi, edited by Shaykh al-Ta'ifah al-Tusi, referred to in the notes as K.

The traditions selected here have been numbered, and the serial number of each tradition in Usul al-Kafi is also mentioned after its serial number in this selection. The part of hadith pertaining to sanadhas been typeset separately in smaller characters so that the reader not interested in sanad can turn to the text of a hadith directly. For those readers interested in information about the standing of narrators, some details about the sources affirming their reliability have been given in tile notes at the end. Al-Kulayni is usually placed in the 9th tabaqh (generation) of narrators.

The tabaqah of each narrator is indicated after his name in the notes. For instance, 5/VI, indicates that the narrator belongs to the 5th tabaqah and has met and narrated from the Sixth Imam, Ja'far al-Sadiq (A). A zero instead of a Roman numeral indicates that he has not narrated directly from any of the Imams. `N353' means, for instance, page 353 of Rijal al Najashi. Other symbols pertaining to books ofrijal have been explained in the bibliography.

For information about al-Kulayni's life and works, refer to the article "Introduction to Imamiyyah Scholars: Al-Kulayni and His works," by Dr. Wahid Akhtar in al-Tawhid, vol.II, No. 3.

At times at the beginning of a sanad, al-Kulayni cites his immediate sources with the phrase عَن عدًةٍ مِن اصحابِنا (from a group of our companions), indicating that he received the tradition from a group of his teachers, who are identifiable from the teacher from whom they narrate. Thus when al-Kulayni says, "A group of our companions, from Ahmad ibn Muhammad ibn `Isa," one or more of the following five pupils of Ahmad ibn Muhammad ibn `Isa are meant:

1. Abu Ja'far Muhammad ibn Yahya al-`Attar al-Qummi.
2. `Ali ibn Musa ibn Ja'far al-Kamandani.
3. Abu Sulayman Dawud ibn Kawrah al-Qummi.
4. Abu `Ali Ahmad ibn Idris ibn Ahmad al-'Ash'ari al-Qummi.
5. Abu al-Hasan `Ali ibn Ibrahim ibn Hashim al-Qummi.

When al-Kulayni says, "A group of our companions, from Ahmad ibn Muhammad ibn Khalid al-Barqi," the following four pupils of al Barqi are meant:

1. Abu al-Hasah `Ali ibn Ibrahim al-Qummi.
2. Muhammad ibn `Abd Allah ibn Udhaynah.
3. Ahmad ibn `Abd Allah ibn Umayyah.
4. `Ali ibn al-Husayn al-Sa'dabadi.

When al-Kulayni says, "A group of our companions, from Sahl ibn Ziyad," he means the following four of Sahl's pupils:

1. Abu al-Hasan `Ali ibn Muhammad ibn Ibrahim ibn Aban al-Razi, known as `Allan al-Kulayni.
2. Abu al-Husayn Muhammad ibn Abi `Abd Allah Ja'far ibn Muhammad ibn 'Awn al-'Asadi al-Kufi, resident at Ray.
3. Muhammad ibn al-Hasan ibn Farrukh al-Saffar al-Qummi.
4. Muhammad ibn `Aqil al-Kulayni.

When al-Kulayni says, "A group of our companions from Ja'far ibn Muhammad, from al-Hasan ibn `Ali ibn Faddal", one of them is Abu `Abd Allah al-Husayn ibn Muhammad ibn `Imran ibn Abi Bakr al 'Ash'ari al-Qummi.