The question in the title is asked constantly and answered badly in both directions — by people who treat a school as though departing from it were departing from Islam, and by people who dismiss the Imams as an obstacle between themselves and the texts. This book examines the underlying principle instead.
The Argument
The author's starting point is straightforward: neither Allah nor His Messenger ﷺ commanded us to follow anybody's opinions and interpretations. Opinions are just that. They may be correct or incorrect, which is why the Imams — working with the same texts, in good faith, with far more learning than most who invoke them — reached different conclusions on many issues. Each explained his position by his own reasoning, and their reasoning differed.
If the positions conflict, they cannot all be what Allah intended. So the standard has to be something prior to all of them, and the texts identify what it is:
"But no, by your Lord, they can have no faith until they make you judge in all disputes between them, and find in themselves no resistance against your decisions, and accept them with full submission." (Surah An-Nisa 4:65)
And the Prophet ﷺ said that he left behind two things which, held to firmly, mean a person will never go astray: the Book of Allah and his Sunnah.
What It Is Not Arguing
This is worth stating, because the discussion is routinely caricatured. The book is not an attack on the four Imams, and it is not a claim that an untrained reader should derive rulings from a translation. The distinction it draws is between benefiting from a scholar's work — which every Muslim must do — and binding yourself to his conclusions in advance, so that a clear proof from the Sunnah cannot move you. The Imams themselves warned against the second, and the book quotes them saying so.
Who It Is For
Muslims who have encountered the argument between schools and want the principles rather than a side. Students of knowledge beginning usul. Anyone told that following evidence over their inherited school is arrogance, or conversely that the schools are worthless. Concise, and it stays on the principle.
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