As for his question, “Is the predominant probability reached by a mujtahid sufficient in such matters, or must one attain decisive certainty?”, the answer is that the issue requires nuance and differentiation. Although some scholastic theologians claim that every informative doctrine—what they label the “fundamentals”—must be held with absolute certainty, that no evidence short of conclusive proof may be cited, and that this level of certainty is required of every individual, their sweeping assertion flatly contradicts the Qur’an, the Sunnah, and the unanimous consensus of the early generations and their leading imams.

Moreover, they themselves are furthest from the standard they set: time and again they rely on arguments they deem definitive which are, in reality, no more than puzzles, let alone probabilistic proofs. It is common to find one of them proclaiming a particular argument sound in one context and confidently declaring it void in another; indeed, some of them never rise above this contradiction. It can even happen that each of two disputants will claim self-evident knowledge of the exact opposite of what his opponent asserts.

The correct, detailed view is this: in any matter where Allah has obligated knowledge and certainty, then whatever degree of knowledge and certainty He has mandated is indeed required. Allah says, “Know that Allah is severe in punishment, yet Allah is Forgiving and Merciful” (Q 5:98), and He says, “So know that there is no deity but Allah, and seek forgiveness for your sin” (Q 47:19). In the same way, faith is obligatory in everything Allah has commanded us to believe.

At the same time, the Sharia has established that every obligation is conditioned by the servant’s capacity. Allah says, “So fear Allah as much as you are able” (Q 64:16), and the Prophet ﷺ said, “When I command you to do something, do of it what you are able” — a report transmitted by both al-Bukhari and Muslim.