Islamic sciences

The celebrated Islamic scholar Abu Hamid Al-Ghazali wrote on Islamic sciences in his well known book The Revival of Religious Sciences (Ihya `ulum al‑din). He argued that a Muslim has a religious obligation (wajib) to know whatever aspects of religious science are necessary for them to obey Shari'ah in doing whatever work it is they do. So, for example, someone working in animal husbandry should know rules concerning zakat; a merchant "doing business in an usurious environment", should learn rules about riba so as "to effectively avoid it". Sciences whose knowledge is wajib kifa'i (must be known by some people in society, although once enough people have met the obligation, the rest of the population is relieved of it).

Al‑Ghazali considers wajib kifa'i religious sciences to be classified into four groups:

1. Usul (principles; i.e. the Qur’an, the sunnah, ijma` or consensus and the traditions of the Prophet's companions)
2. Furu` (secondary matters; i.e. problems of jurisprudence, ethics and mystical experience)
3. Introductory studies (Arabic grammar, syntax, etc.)
4. Complementary studies (recitation and interpretation of the Qur’an, study of the principles of jurisprudence, `ilm al‑rijal or biographical research about narrators of Islamic traditions etc.)