Kilichomsaidia al-Shafi'i kuweka misingi ya elimu ya usul ni kwamba alikuja wakati ambapo fiqh ya Kiislamu ilikuwa imeanza kustawi sana. Katika nchi za Kiislamu vikundi vya kijaji vya mujtahidina vilianza kujitokeza, na vikaanza kujipanga kuwa mazhabu (madhehebu). Mjadala kati ya Mujtahidina na wafuasi wa mazhabu ulichukua mitazamo mbalimbali katika fiqh na dalili. Hivyo, alijitosa katika mijadala pamoja na wale waliojihusisha na mdahalo huo, na mijadala hii ndiyo iliyomwongoza kufikiri kuhusu kanuni za jumla na zenye kukamilika kama vigezo vya kusimamia, ambavyo vinapaswa kuwa msingi wa utafiti na uhitimishaji. Aliviunganisha kanuni hizi kuwa mwili mmoja wa maarifa, ambao ndio elimu ya usul al-fiqh.
Jambo la kuvutia kuhusu usul za al-Shafi'i ni kwamba anaendelea katika majadiliano ya usul kwa njia ya kisheria na si kwa njia ya kimantiki. Mojawapo ya hatari kubwa kwa utafiti, na kwa kweli kwa uhuishaji wa Ummah hasa katika fiqh na usul, ni njia ya mantiki. Al-Shafi'i alijitenga wazi na mwelekeo wa mantiki na kushikamana na mwelekeo wa kisheria. Hakuvutiwa na mbinu za kinadharia wala dhana. Alitaka kusimamia masuala halisi na yaliyopo, yaani, alichukua matini za Sharī'ah na kusimama katika mpaka wa matini hiyo na katika mpaka wa uhalisia ambao matini ilionyesha na ambao watu wenyewe walishuhudia.
Kuhusu suala la kufuta hukumu (naskh wal mansukh), alianzisha kanuni za kufuta kutoka katika masuala ambayo, kwa mtazamo wake, yalikuwa yamethibitika kuwa na kufutwa kwa hukumu, zilizotolewa kutoka kile kilichotajwa katika aya au hadithi yenyewe, au kutoka dalala (dalili) ya kufutwa, au kutoka kile kilichosimuliwa kuhusu Mtume katika hadithi zinazoonyesha kufutwa, au chochote kilichopokewa kuhusu Maswahaba wa Mjumbe wa Allah katika mapokezi na hukumu. Tofauti na wengi waliokuja baada yake, ambao walipoona mkinzano kati ya aya mbili au hadithi mbili walikimbilia mara moja kusema kwamba moja imeifuta nyingine, hadi wakafanya makosa makubwa mno, al-Shafi'i alipoleta kanuni hakuitoa katika msingi wa kimantiki (muqaddima mantiqiyya), bali alionyesha vyanzo ambavyo aliichukulia, iwe kutoka kwenye hadithi ya Mtume ﷺ au kutoka kwenye fatwa za Maswahaba. Mbinu yake katika kuchota kanuni za kisheria (qawa'd dabita) ilikuwa ya vitendo, ambapo alitegemea uhalisia, dalili, na matumizi ya mambo hayo juu ya ukweli unaoonekana.
Jambo lililo mashuhuri zaidi linalotofautisha usul ya Shafi'i ni kwamba ina kanuni za jumla za istinbat (kuchota hukumu), bila kujali mbinu yake maalum ilikuwa ipi. Zaidi ya hayo, usul yake inafaa kwa mbinu yoyote, hata iwe tofauti kiasi gani. Hivyo, ni kipimo ambacho kwacho mtu anaweza kujua ni maoni yapi ni sahihi na yapi si sahihi. Ni sheria pana ambayo lazima izingatiwe wakati wa kuchota hukumu mpya, kwa mbinu yoyote mtu atakayojiwekea, ili kupima maoni na kudhibiti uchotaji wa hukumu kwa sheria pana.
Usul ya al-Shafi'i haikukusudiwa kuwa usul ya mazhabu yake peke yake, ingawa mazhabu hiyo iliifuata. Haikuandikwa kuitetea mazhabu yake na kufafanua msimamo wake. Badala yake, ina kanuni za jumla na pana za istinbat. Lengo halikuwa mwelekeo kwa mazhabu fulani, bali lilikuwa hamu ya kudhibiti taratibu za Ijtihad na kuweka mipaka na miongozo kwa mujtahidina. Alikuwa mkweli katika nia zake, na alikuwa na ufahamu sahihi alipoanzisha elimu ya usul al-fiqh, na hivyo akaathiri, bila ubaguzi, mujtahidina na ‘Ulamā waliokuja baada ya al-Shafi'i, iwe walipinga maoni yake au waliyaunga mkono. Hadi walipoona, licha ya tofauti za mielekeo yao, kwamba wanaendelea kufuata njia aliyoifuata al-Shafi'i, katika kuweka kanuni kuu pana (qawa'id kulliyya) na kuendelea katika fiqh na istinbat (kuchota hukumu) kwa mpangilio maalum kwa kufuata sheria za jumla na kanuni za msingi. Fiqh (elimu ya sheria ya Kiislamu) baada yake ikaja kujengwa juu ya misingi iliyothibitishwa, si kama mkusanyiko wa fatwa na hukumu za kibinafsi (aqdiya) kama ilivyokuwa kabla yake. Ingawa Maulamaa wote wanafuata nyayo za al-Shafi'i kuhusu dhana ya usul al-fiqh, lakini namna walivyopokea yale aliyoyafikia al-Shafi'i ilitofautiana kulingana na mitazamo yao tofauti ya kifiqhi. Baadhi walifuata maoni yake na kuanza kuyafafanua na kuyapanua na kutofautiana nayo, kama wafuasi wa al-Shafi'i mwenyewe. Na wengine walichukua sehemu kubwa ya yale aliyoleta al-Shafi'i licha ya kutofautiana naye katika baadhi ya maelezo ya usul, lakini hawakuchukua msingi halisi wa usul. Kwa kuwa hawakutofautiana katika msingi, muundo na mwelekeo wa usul ya al-Shafi'i, kama Hanafi na wale waliofuata mbinu yao. Na kuna waliotofautiana na al-Shafi'i katika usul hii, kama Dhahiriyya na Shia. Waliomfuata al-Shafi'i katika maoni yake ni Hanbali. Walichukua usul ya al-Shafi'i ingawa walisema kwamba ijma' (makubaliano) pekee (inayotambulika) ni ya Masahaba. Maliki waliokuja baada ya al-Shafi'i waliunganisha mbinu yao na sehemu kubwa ya yale yaliyomo katika usul ya al-Shafi'i, ingawa walichukua mwenendo wa watu wa Madina kuwa ni hoja na wakatofautiana naye katika baadhi ya maelezo. Kwa upande wa wale waliofuata mbinu yake na kukubali maoni yake, ni wafuasi wa madhehebu yake ambao walikuwa hai sana katika elimu ya usul al-fiqh na waliandika kwa wingi kuhusu somo hilo. Vitabu viliandikwa kwa kufuata mbinu ya al-Shafi’i katika usul al-fiqh, ambavyo vilikuwa, na bado ni, nguzo na msingi wa elimu hii. Miongoni mwa vitabu vitatu muhimu zaidi vinavyojulikana kuwa viliandikwa na wanazuoni wa zamani: La kwanza, kitabu al-Mu’tamad cha Abu al-Husayn Muhammad ibn al-Basri (d. 413 A.H.); la pili, kitabu al-Burhan cha ‘Abd al-Malik ibn ‘Abd Allah al-Juwayni, maarufu kama imam al-Harāmayn (d. 478 A.H.); na la tatu, kitabu al-Mustasfa cha Abu Hamid al-Ghazali (d. 505 A.H.).
Baada yao alikuja Abu al-Husayn ‘Ali, almaarufu kama al-Amidi. Yeye alivikusanya vitabu vyote vitatu na kuvipanua katika kitabu chake al-Ihkam fi usul al-ahkam, ambacho kilikuwa mojawapo ya kazi muhimu zaidi zilizoandikwa katika usul al-fiqh.
Kuhusu wale waliokubali sehemu kubwa ya yale aliyoleta al-Shafi’i na kutofautiana katika baadhi ya maelezo, ni Mahanafi. Hiyo ni kwa sababu mbinu yao ya istinbat (kuchota hukumu) ilikubaliana na usul za al-Shafi’i, ingawa njia waliyoitumia kuishughulikia elimu ya usul iliathiriwa na furu’ (matawi ya fiqh). Walisoma kanuni za usul ili kuunga mkono furu’. Hivyo wakazifanya furu’ kuwa msingi; kanuni za jumla zikawekwa juu yake na kufanywa ziitegemeze. Huenda kilichowasukuma kwenye mbinu hii ni kwamba utafiti wao wa usul ulikuwa kwa lengo la kuunga mkono mazhabu yao, si kwa lengo la kutoa kanuni ambazo madhehebu yao yangechota hukumu. Hiyo ni kwa sababu Abu Hanifa, aliyemtangulia al-Shafi’i, alifariki mwaka ambao al-Shafi’i alizaliwa, na hukumu zake hazikuwa kwa kufuata kanuni za jumla na zenye kukusanya. Vilevile baada yake walikuja wanafunzi wake Abu Yusuf, Muhammad na Zufar. Hawakujishughulisha na kuandika kuhusu usul al-fiqh, bali ilikuja kuwa jukumu la wanazuoni wa mazhabu ya Kihanafi baadaye kutafuta kuchota kanuni zitakazotumikia furu’ za mazhabu ya Kihanafi. Kanuni hizo zilikuja baadaye kuliko furu’ na hazikutangulia. Hata hivyo, misingi ya usul ya Hanafi kwa ujumla imetolewa kutoka katika usul za al-Shafi'i. Na yale waliyotofautiana nayo na Washafi'i kuhusu kuwa ya jumla ('aamm) ni ya uhakika (qat'i) kama ilivyo ya mahsusi (khas).
What helped al-Shafi’i to lay down the science of usul was that he came at a time when Islamic jurisprudence had started to greatly flourish. In the Islamic lands juristical groups of mujtahidin began to take shape and they began to form into mazhabs (schools). The debate between the Mujtahidin and the proponents of mazahibs took various perspectives in fiqh and the evidences. So he plunged into debates with those who engaged in the debate, these discussions were what guided him to think about general and comprehensive principles as regulatory criterions which should be the basis of study and inference. He brought together these principles as one body of knowledge which was the science of usul al-fiqh. The impressive thing about the usul of al-Shafi’i is that he proceeds in the discussion of usul in a legislative and not in a logical manner. One of the greatest dangers for study, in fact for the Ummah’s revival especially in fiqh and usul is the path of logic. Al-Shafi’i clearly distanced himself from the course of logic and adhered to the legislative course. He was not interested in theoretical methods or suppositions. He wanted to regulate real and existing issues i.e, he took the Sharī’ah texts and stopped at the limit of the text and at the limit of the reality which the text indicated and the people themselves witnessed. Regarding the issue of abrogation (nasikh wal mansukh), he established the principles of abrogation from the issues which, for him, had been proven to contain abrogations, taken from what has been mentioned in the ayah or hadīth itself, or from the indication (dalala) of abrogation, or what has been narrated about the Messenger in terms of hadīth which indicate abrogation or whatever has been reported about the Companions of the Messenger of Allah in terms of reports and judgements. Not like many who came after him when they saw a contradiction between two verses or ahadīth they immediately moved to say that one has abrogated the other, to the extent that they ended up making terrible blunders. When al-Shafi’i came with a principle he did not bring it from a logical premise (muqaddima mantiqiyya) rather he showed the sources from which he took it, either from a report about the Prophet or from legal verdicts (fatwas) of the Sahabah. His approach in deriving regulatory (qawa’d dabita) principles was a practical one in which he relied on the reality, the evidences, and on the application of those things on tangible facts. The most prominent aspect by which Shafi’is usul is distinguished is that it contains general principles for the deduction (istinbat) of rules, regardless of what his specific methodology was. Rather, his usul is suitable for any methodology however different it may be. Thus, it is a measure by which one can know which opinions are correct and which are not correct. It is a comprehensive law which must be adhered to when deducing new rules, whatever methodology a person may set himself, in order to judge opinions and regulate the inference of rules by a comprehensive law. The usul of al-Shafi’i was not intended to be an usul for his mazhab (school) only, even though the mazhab adhered to it. It was not written to defend his mazhab and clarify its viewpoint. Rather, it contains general and comprehensive principles for istinbat (inference). The motive was not a trend towards a particular mazhab but rather it was a desire to regulate the procedures of Ijtihād and put in place limits and guidelines for the mujtahidin. He was sincere in his intentions and he had the correct understanding when devising the science of usul al-fiqh, thereby influencing, without exception, those mujtahidin and ‘Ulamā that came after al-Shafi’i, whether they opposed or supported his opinions. Until, despite their different tendencies, they saw themselves proceeding according to the path al-Shafi’i had taken, in terms of setting out comprehensive principles (qawa’id kulliyya) and proceeding in fiqh and istinbat (inference) in a regulated manner according to comprehensive laws and general principles. Fiqh (Islamic jurisprudence) after him came to be based on established foundations not as an assortment of fatwas and individual judgements (aqdiya) as was the case before him. Even though all of the ‘Ulamā proceed in the footsteps of al-Shafi’i in terms of the notion of usul al-fiqh, however the way in which they received what al-Shafi’ had arrived at was different according to their different juristic approaches. Some followed his opinions and began to explain and expand on them and disagree with them, like the followers of al-Shafi’i himself. And some took the major part of what al-Shafi’i had brought despite their disagreement with certain details of usul and but not the actual body of usul. Since they had no disagreements in terms of the body, framework and course of al-Shafi’is usul, like the Hanafis and those who followed their method. And there were those who disagreed with al-Shafi’i in this usul, like the Zahiris and Shi’a. Those who followed al-Shafi’i in his opinions were the Hanbalis. They adopted the usul of al-Shafi’i even though they said the only (recognised) ijma’ (consensus) is that of the Sahabah. The Malikis who came after al-Shafi’i combined their methodology with much of what was in al-Shafi’i’s usul though they took the practise of the people of Madina as a proof and differed with him in certain details. As for those who proceeded according to his method and embraced his opinions they are the followers of his mazhab who were very active in the (study of) the science of usul al-fiqh and wrote prolifically about the subject. Books were written according to the methodology of al-Shafi’i in usul al-fiqh which were, and still are, the pillars and support of this science. Of the most important three books that are known to be written by the ancients: First, the book al-Mu’tamad of Abu al Husayn Muhammad ibn al-Basri (d.413 A.H.), Second, the book al-Burhan of ‘Abd al-Malik ibn’ Abd Allah al-Juwayni commonly known as imam al-Harāmayn (d.478 A.H.) and third, the book al-Mustasfa of Abu Hamid al-Ghazali (d.505 A.H). After them came Abu al-Husayn ‘Ali otherwise known as al-Amidi. He brought together all three books and expanded on them in his book al-ihkam fi usul al-ahkām, which was one of the most important works written on usul al-fiqh, as for those who adopted the major part of what al-Shafi’i brought and differed in some of the details, they are the Hanafis. That is because their method of istinbat (inference) agreed with the usul of al-Shafi’i though the way in which they approached the science of usul was influenced by the furu’ (branches of fiqh). They studied the principles of usul in order to support the furu’. So they made the furu’ the basis. The general principles were based on it and made to support it. Perhaps what pushed them towards this approach was that their study of usul was for the purpose of supporting their mazhab and not in order to produce principles according to which their school should deduce rules. That is because Abu Hanifa who had preceded al-Shafi’i, died the year in which al-Shafi’i was born. And his inferences were not according to general and comprehensive principles. Likewise after him came his students Abu Yusuf, Muhammad and Zufar. They did not concern themselves with writing about usul al-fiqh but it fell to the scholars of the Hanafi mazhab afterwards to pursue the inference of principles which would serve the furu’ of the Hanafi mazhab, The principles came later than the furu’ and did not precede it. Nevertheless, the Hanafi usul on the whole has been extracted from the usul of al-Shafi’i. And what they differed on with the Shafi’is in terms of the ‘aamm (general) being qat’i (definite) like the khas (specific),