Ilm al-kalam or ilm al-lahut, often shortened to kalam, is the scholastic, speculative, or rational study of Islamic theology (aqida). It can also be defined as the science that studies the fundamental doctrines of Islamic faith (usul al-din), proving their validity, or refuting doubts regarding them. Kalām was born out of the need to establish and defend the tenets of Islam against philosophical doubters and non-Muslims, Madeleine Pelner Cosman, Linda Gale Jones, Handbook to Life in the Medieval World, p. 391. and also to defend against heretical and religious innovations (bidʿah).Abul Quasem, M. (1975). The ethics of al-Ghazali: A composite ethics in Islam. p. 18 A scholar of kalam is referred to as a mutakallim (plural mutakallimun), a role distinguished from those of Islamic philosophers and jurists.Clinton Bennett, The Bloomsbury Companion to Islamic Studies, p. 119. .

After its first beginnings in the late Umayyad period, the Kalām experienced its rise in the early Abbasid period, when the Caliph al-Mahdi commissioned Mutakallimūn to write books against the followers of Iranian religions, and the Barmakid vizier Yahya ibn Khalid held Kalām discussions with members of various religions and confessional groups in his house. By the 10th century, the Muʿtazilites were main pioneers of 'Kalam' during the early formative period of Islam. Soon after, two new important Sunni Kalām schools emerged: the Ashʿaris and the Maturidis. They positioned themselves against the growing Neoplatonic and Aristotelian philosophy within the Mu'tazilites and elevated the "Kalām science" (ʿilm al-kalām) as an acceptable ranking science in mainstream Sunni discourse. Some of the arguments of these Mutakallimūn also found their way into Jewish and Christian theological discussions in the Middle Ages. Kalām science by the early modern period was essentially limited to the study of manuals and commentaries, from the late 19th century onwards various reform thinkers appeared in British India and the Ottoman Empire who called for the founding of a "new Kalām".

Definition Definitions of Kalām in chronological order Author with death date Region Kalām is... Arabic or Persian original text al-Farabi (d. 950) Syria "a mental ability through which man can help the established views and actions expressed by the founder of a religion to triumph and can refute everything that contradicts them by statements" malaka yaqtadir bi-hā al-insān ʿalā nuṣrat al-ārā wa-l-afʿāl al-maḥdūda allatī ṣarraḥa bi-hā wāḍiḥ al-milla wa-tazyīf kull mā ḫālafa-hā bi-l-aqāwīl Abu al-Hassan al-Amiri (d. 992) Baghdad, Nishapur "the linguistic effort to defend religion" al-muǧāhada ʿan ad-dīn bi-l-lisān Abu Hayyan al-Tawhidi (d. 1023) Baghdad, Rayy, Shiraz "a way of considering the foundations of religion, in which the deliberation is based on reason alone." bāb min al-iʿtibār fī uṣūl ad-dīn yadūr an-naẓar fīhi ʿalā maḥḍ al-ʿaql Abu al-Yusr al-Bazdawi (d. 1099) Transoxiana "the explanation of those questions which constitute the foundations of religion, which it is an individual duty to learn." bayān al-masāʾil allatī hiya uṣūl ad-dīn allatī hiya taʿallumuhā farḍ ʿainSharaf al-Din Ibn al-Tilimsani al-Fihri (d. 1260) Egypt "the knowledge of the evidence of divinity and divine messengership, as well as the things on which their knowledge depends, namely the possibility and temporal origin of the world and the refutation of everything that is incompatible with this" al-ʿilm bi-ṯubūt al-ilāhīya wa-r-risāla wa-mā yatawaqqaf maʿrifatuhumā ʿalaihi min ǧawāz al-ʿālam wa-ḥudūṯihī wa-ibṭāl mā yunāqiḍ ḏālik Shams al-Din al-Samarqandi (d. 1303) Samarkand "a science that investigates the nature and attributes of God and the states of contingent entities in the beginning and at the return according to the law of Islam" ʿilm yubḥaṯ fīhi ʿan ḏāt Allāh wa-ṣifātihī wa-aḥwāl al-mumkināt fī l-mubtadaʾ wa-l-maʿād ʿalā qānūn al-islām Adud al-Din al-Iji (d. 1355) Īj near Shiraz "the science by which one can prove religious dogmas by citing arguments and averting doubts" ʿilm yuqtadar maʿa-hū ʿalā iṯbāt al-ʿaqāʾid ad-dīnīya, bi-īrād al-ḥuǧaǧ wa-dafʿ aš-šubah al-Taftazani (d. 1390) Taftazan "the knowledge of religious dogmas based on certain evidence" al-ʿilm bi-l-ʿaqāʾid ad-dīnīya ʿan al-adilla al-yaqīnīya Ibn 'Arafa (d. 1401) Tunis "the knowledge of the decrees of divinity, the sending of messengers, their truthfulness in all their communications, and that on which any of them is specifically based, as well as the establishment of their proofs by a skill that is believed to avert doubts and resolve uncertainties" al-ʿilm bi-aḥkām al-ulūhīya wa-irsāl ar-rusul wa-ṣidqihā fī kull aḫbārihā wa-mā yatawaqqaf šaiʾ min ḏālik ʿalaihi ḫāṣṣan bihī wa-taqrīr adillatihā bi-qūwa hiya maẓinna li-radd aš-šubuhāt Ibn Khaldun (d. 1406) Tunis "a science that involves the disputation of religious dogmas with rational arguments and the refutation of innovators who deviate from the teachings of the ancients and the Sunnis." ʿilm yataḍamman al-ḥiǧāǧ ʿan al-ʿaqāʾid al-īmānīya bi-l-adilla al-ʿaqlīya wa-r-radd ʿalā l-mubtadiʿa al-munḥarifīn fī l-iʿtiqādāt ʿan maḏāhib as-salaf wa-ahl as-sunna Ibn al-Humām (d. 1457) Egypt "the knowledge of the individual about the dogmas of the Islamic religion that are incumbent upon him through the evidence" maʿrifat an-nafs mā ʿalaihā min al-ʿaqāʾid al-mansūba ilā dīn al-islām ʿan al-adilla Taşköprüzade (d. 1561) Ottoman Empire "the science of proving religious truths by providing arguments for them and removing doubts from them" ʿilm yuqtadar maʿa-hū ʿalā iṯbāt al-ḥaqāʾiq ad-dīnīya, bi-īrād al-ḥuǧaǧ ʿalai-hā wa-dafʿ aš-šubah ʿan-hā Abd al-Razzaq Lahiji (d. 1661) Iran "a theoretical skill with which one can prove religious dogmas" ṣināʿa naẓarīya yuqtadar bi-hā ʿalā iṯbāt al-ʿaqāʾid ad-dīnīya al-Tahānawī (d. 1745) North India "a science by which one can prove religious dogmas to one's fellow men by citing arguments and averting doubts" ʿilm yuqtadar maʿa-hū ʿalā iṯbāt al-ʿaqāʾid ad-dīnīya ʿalā l-ġair, bi-īrād al-ḥuǧaǧ wa-dafʿ aš-šubah. Morteza Motahhari (d. 1979) Iran "a science that discusses Islamic dogmas, i.e. what one must believe in from an Islamic point of view, in such a way that it explains, proves and defends them" ʿilmi ast ke darbāre-ye ʿaqāyed-e eslāmī yaʿnī ānče az naẓar-e eslām bāyad bedān moʿtaqed būd va īmān dāšt, baḥs̱ mīkonad be īn naḥw ke ānhā toużīḥ mīdehad va darbāre-ye ānhā estedlāl mīkonad va az ānhā defāʿ mīnamāyad

Kalām as apologetics According to several of the definitions given above, kalām has an apologetic function: it serves to defend one's own religious views. This apologetic function is particularly evident in the philosophers al-Farabi (d. 950) and Abu al-Hassan al-Amiri (d. 992). The former sees it as a mental ability through which man can refute everything that contradicts the views and actions established by the founder of the religion, the latter as "the defence of religion with the tongue". In the definitions of the Ashʿarite scholar Adud al-Din al-Iji (d. 1355), the Ottoman scholar Taşköprüzade (d. 1561) and the Indian scholar at-Tahānawī (around 1745), who worked in Iran, kalām has the task of averting doubts from religious dogmas or truths. Against the background of such definitions, the French orientalist Louis Gardet judged that the function of kalām as a defensive "apology" could not be overestimated. The view that the "fundamental character" of the Kalām consists of "defensive apology" is also the declared leitmotif of the French handbook Introduction à la théologie musulmane, co-authored by Gardet and M.M Anawati in 1948.

The Indian scholar ʿAbd an-Nabī al-Ahmadnagarī (d. 1759) even believed that the value of the Kalam was limited to this apologetic function alone. The great Mutakallimūn, he explains in his encyclopedia Dustūr al-ʿulamā, never justified or authenticated their doctrines with arguments from the Kalam, since the sole purpose of the Kalam was to silence the adversary and bring the stubborn to their knees. The great Mutakallimūn, on the other hand, drew their doctrines solely from the "lamp of prophethood". Such statements can also be found in al-Ghazali. Thus, in his work Jawahir al-Qur'an (The Jewels of the Qur'an ), he judged that the purpose of the science of kalam was "to protect the beliefs of the masses from disruption by innovators". On the other hand, this science was never about "revealing the truths".

Kalām as the science of religious foundations or dogmas Several Muslim authors defined kalām by its relationship to the "fundamentals of religion" (Uṣūl al-Dīn). For example, Abu Hayyan al-Tawhidi (d. 1023) described the science of kalām as "a way of contemplating the fundamentals of religion in which deliberation is based on reason alone." Abu al-Yusr al-Bazdawi (d. 1099) defined it as "the explanation of those questions which constitute the fundamentals of religion, which it is an individual duty to learn."

Ibn al-Athir (d. 1233) in his book al-Lubāb fī Tahḏīb al-Ansāb was the first to define kalām science as "the science of the foundations of religion" (ʿilm Uṣūl al-Dīn). Ibn Khallikan (d. 1282) and Siraj al-Din Urmavi (d. 1283) even equated kalām science with the foundations of religion itself. The equation of ʿilm al-kalām and ʿilm uṣūl al-dīn is also found in the catalogue of the Ottoman Palace Library from the beginning of the 16th century, where the section containing the books on kalām was entitled "Section of the Books of the Science of the Foundations of Religion, i.e. the Science of Kalām". This classification probably also influenced the Ottoman scholars Taşköprüzade and Saçaklızāde (d. 1732), who also equated kalām science and the "science of the foundations of religion" in their Arabic scientific encyclopedias. At-Tahānawī explains this equation by saying that the Kalām is the basis of the religious legal sciences and that they are based on it.

Some later scholars defined the kalām science of dogmas. For Adud al-Din al-Iji (d. 1355), kalām is "the science of proving religious dogmas by citing arguments and removing doubts." In a slightly modified form, this definition was also adopted by the Ottoman scholar Tashköprüzāde (d. 1561) and the Indian scholar at-Tahānawī (c. 1745). For al-Taftazani (d. 1390), Kalām is "the knowledge of religious dogmas based on certain evidence", for Ibn Khaldun (d. 1406) "a science that includes the disputation of the dogmas of faith with rational arguments" and for Morteza Motahhari (d. 1979) "a science that discusses the Islamic dogmas [...] in such a way that it explains, proves and defends them".

Theories about the origin of the term In Arabic, the term Kalām generally means "speech, conversation, debate." There are different theories as to why this term came to be used to describe the discipline that deals with the rational justification of one's own religious doctrines:

Al-Shahrastani (d. 1153) suggested that the name was coined by the Mu'tazila. They called this science by this name either because the speech of God was the main question around which their disputations and controversies revolved, so that the whole science was called by it. Ibn at-Tilimsanī (d. 1260) considered three different possibilities: 1. the name Kalām comes from the fact that the Mutakallimūn began the chapters in their books with the phrase: "Chapter of speech about..." ( bāb al-kalām fī... ); 2. When the Zahirites were asked about one of the problems of this science, they replied: "That is that about which we are forbidden to speak". This happened repeatedly, so that after a time it was called "the science of (forbidden) speech", with the expression "forbidden" eventually being dropped; 3. Science was called ʿilm al-kalām because its learning is one of the most important means of bringing out the intellectual power of speech by which man is distinguished from other living beings.