Faith — Its Definition, Increase, and the Question of Major Sins

The final major theological section of al-Aqeedah al-Tahawiyyah addresses the definition of faith (iman), its increase and decrease, and the important doctrinal question of what happens to a Muslim who commits a major sin — a question that has historically divided the Muslim ummah into several distinct theological camps.

Al-Tahawi defines faith in the comprehensive Sunni manner: 'Faith is affirming with the heart, confessing with the tongue, and acting with the limbs.' This three-part definition, while standard in Sunni theology, is not without internal nuance. The Murji'a — a historical group accused of theological laxity — defined faith as belief of the heart alone, arguing that actions were not part of faith itself and thus could not increase or decrease it. On the opposite extreme, the Khawarij defined faith so strictly that any major sin would constitute apostasy. Al-Tahawi steers the Sunni middle course: faith is a unified reality encompassing conviction, declaration, and action, and while actions are integral to faith, their absence or deficiency does not expel a believer from Islam.

Regarding increase and decrease of faith, al-Tahawi affirms the Sunni doctrine that faith increases with obedience and decreases with sin. The Quran itself speaks of faith increasing: 'And whenever a surah was revealed, some of them said: Which of you has this increased in faith? As for those who believed, it has increased them in faith while they rejoice' (Quran 9:124). The believer's faith is not a fixed quantity but a dynamic spiritual state that grows through acts of worship, remembrance, reflection, and righteous action, and diminishes through sin, heedlessness, and disobedience.

The question of the major sinner (murtakib al-kabirah) is addressed directly. Al-Tahawi states: 'We do not consider any of the people of our qiblah (Muslims) to be unbelievers on account of any sin, as long as they do not consider it permissible.' This is the Sunni position against the Khawarij, who declared Muslims who committed major sins to be apostates deserving of death. The Khawarij position produced devastating consequences historically, being used to justify violence against the Muslim community, and its theological basis — that faith is an all-or-nothing proposition that evaporates with any major sin — is refuted by numerous Quranic verses and hadiths that address the believer who sins without calling them an unbeliever.

Al-Tahawi also affirms the possibility of the forgiveness of major sins for believers. If a person died without repentance, they are under the will of Allah: if He wills, He forgives them through His mercy; if He wills, He punishes them for their sin and then eventually enters them into Paradise. This is established by the verse: 'Indeed, Allah does not forgive shirk, but He forgives what is less than that for whom He wills' (Quran 4:48). The assurance of ultimate salvation for any believer who dies upon Tawhid — even after punishment in Hellfire proportionate to their sins — is a core Sunni doctrine of hope and mercy, sharply distinguished from the Mu'tazili and Khariji positions that would consign major sinners to eternal damnation.