The Maxims of Certainty and Doubt

The second universal legal maxim — 'Certainty is not removed by doubt' (al-yaqin la yazul bish-shakk) — is among the most practically important principles in Islamic law. It establishes the presumption of continuity: the last established legal state continues until there is certain evidence of its change. This principle is grounded in the hadith in which a man complained to the Prophet about feeling as if he had passed wind during prayer, and the Prophet replied: 'Do not leave [the prayer] until you hear a sound or find a smell' (al-Bukhari, Muslim).

The practical applications of this maxim are widespread across all areas of Islamic law. In taharah: if a person is certain they performed wudu and uncertain whether they subsequently broke it, they remain in a state of wudu. If they are certain they broke wudu and uncertain whether they subsequently renewed it, they are considered without wudu. The last certain state continues until there is certainty of its change.

In prayer: if a person is uncertain whether they performed two or three rak'ahs, they assume the lesser number (two) because that is what is certain. They then complete the uncertain rak'ahs on the basis of that assumption. This prevents the prayer from being potentially deficient — it is better to perform an extra rak'ah from a position of certainty than to leave the prayer potentially incomplete based on assumption of a higher number.

In transactions: if a person is uncertain whether they paid a debt they owe, the presumption is that the debt remains outstanding (since the debt was the last established state). Conversely, if a creditor is uncertain whether a known debt was repaid, the debtor's presumption of discharge does not hold — the certainty of the debt's existence is not removed by the creditor's uncertainty about receipt of payment. The burden of proof lies with the party claiming a change from the established state.

In criminal law: the maxim of certainty connects to the principle that 'the original rule for human beings is innocence' (al-asl fi-l-insan al-bara'ah). A person is presumed innocent of any crime until it is established with certainty. This presumption can only be overridden by certain evidence — testimony of the required number of witnesses, confession, or definitive forensic evidence. Mere suspicion or probability does not change the presumption of innocence.

The maxim generates an important sub-maxim: 'What is established by certainty is not removed by doubt; what is established by doubt is removed by certainty.' This refinement addresses situations where there are gradations of evidence: a legal state established through weak evidence (like a single witness) is more vulnerable to challenge than one established through strong evidence (like multiple witnesses or written documentation).

Contemporary applications of this maxim are significant in Islamic finance and medical ethics. In Islamic finance, the presumption of permissibility of transactions until clear evidence of prohibition is a version of the certainty maxim applied to contractual validity. In medical ethics, the certainty of an existing medical condition justifying a treatment takes precedence over the uncertainty of the treatment's long-term effects — the maxim grounds a kind of precautionary principle in medical decision-making.