Logic (Arabic: منطق), or Islamic logic, played an important role in Islamic philosophy. Islamic law and jurisprudence placed importance on formulating standards of argument, which gave rise to a novel approach to logic in Kalam, as seen in the method of qiyas. This approach, however, was later displaced to some extent by ideas from ancient Greek and Hellenistic philosophy with the rise of the Mu'tazili school, who highly valued Aristotle's Organon. The works of Hellenistic-influenced Islamic philosophers were crucial in the reception of Aristotelian logic in medieval Europe, along with the commentaries on the Organon by Averroes, founder of Averroism. In turn, the Aristotelian tradition was later displaced by Avicennian logic, which in turn was succeeded by Post-Avicennian logic.
Important developments made by Islamic logicians included the development of original systems of logic, notably Avicennian and Post-Avicennian logic, and the development of early theories on temporal logic, modal logic,inductive logic,hypothetical syllogism,propositional calculus,analogical reasoning, and legal logic. Other important developments in early Islamic philosophy include the development of a strict science of citation, the isnad or "backing", and the development of a scientific method of open inquiry to disprove claims, the ijtihad, which could be generally applied to many types of questions.
Another important Islamic contribution to modern logic is algebra (see Islamic mathematics), which led to the development of modern algebraic logic in the 19th century. 
According to the Routledge Encyclopedia of Philosophy:
"For the Islamic philosophers, logic included not only the study of formal patterns of inference and their validity but also elements of the philosophy of language and even of epistemology and metaphysics. Because of territorial disputes with the Arabic grammarians, Islamic philosophers were very interested in working out the relationship between logic and language, and they devoted much discussion to the question of the subject matter and aims of logic in relation to reasoning and speech. In the area of formal logical analysis, they elaborated upon the theory of terms, propositions and syllogisms as formulated in Aristotle's Categories, De interpretatione and Prior Analytics. In the spirit of Aristotle, they considered the syllogism to be the form to which all rational argumentation could be reduced, and they regarded syllogistic theory as the focal point of logic. Even poetics was considered as a syllogistic art in some fashion by most of the major Islamic Aristotelians."
"Since logic was viewed as an organon or instrument by which to acquire knowledge, logic in the Islamic world also incorporated a general theory of argumentation focused upon epistemological aims. This element of Islamic logic centred upon the theory of demonstration found in Aristotle's Posterior Analytics, since demonstration was considered the ultimate goal sought by logic. Other elements of the theory of argumentation, such as dialectics and rhetoric, were viewed as secondary to demonstration, since it was held that these argument forms produced cognitive states inferior in certitude and stability to demonstration. The philosopher's aim was ultimately to demonstrate necessary and certain truth; the use of dialectical and rhetorical arguments was accounted for as preparatory to demonstration, as defensive of its conclusions, or as aimed at communicating its results to a broader audience."
Logic in Arabic grammarEdit
Main article: Arabic grammar
Some of the earliest known logic in the Islamic world came from the work of Arabic grammarians. Examples include the grammatical works of Ibn Abi Ishaq (d. 735) and Sibawayh (d. 797). The latter's work in particular has been compared in its logical sophistication to the work of Pāṇini, a Sanskrit grammarian of the Indian tradition.
Logic in Islamic law and theologyEdit
- See also: Qiyas and Kalam
Early forms of analogical reasoning, inductive reasoning and categorical syllogism were introduced in Fiqh (Islamic jurisprudence), Sharia (Islamic law) and Kalam (Islamic theology) from the 7th century with the process of Qiyas, at least a century before Muslims had become aware of Aristotelian logic. The Qiyas process was described by early Islamic legal scholars such as Abū Ḥanīfa (699-765) and Muhammad ibn Idris ash-Shafi`i (767-820). Later during the Islamic Golden Age, there was a logical debate among Islamic philosophers, logicians and theologians over whether the term Qiyas refers to analogical reasoning, inductive reasoning or categorical syllogism. Some Islamic scholars argued that Qiyas refers to inductive reasoning, which Ibn Hazm (994-1064) disagreed with, arguing that Qiyas does not refer to inductive reasoning, but refers to categorical syllogism in a real sense and analogical reasoning in a metaphorical sense. On the other hand, al-Ghazali (1058-1111) (and in modern times, Abu Muhammad Asem al-Maqdisi) argued that Qiyas refers to analogical reasoning in a real sense and categorical syllogism in a metaphorical sense. Other Islamic scholars at the time, however, argued that the term Qiyas refers to both analogical reasoning and categorical syllogism in a real sense.
Ibn Hazm (994-1064) wrote the Scope of Logic, in which he stressed on the importance of senseperception as a source of knowledge. He wrote that the "first sources of all human knowledge are the soundly used senses and the intuitions of reason, combined with a correct understanding of a language." He also criticized some of the more traditionalist theologians who were opposed to the use of logic and argued that the first generations of Muslims did not rely on logic. His response was that the early Muslims had witnessed the revelation directly, whereas the Muslims of his time have been exposed to contrasting beliefs, hence the use of logic is necessary in order to preserve the true teachings of Islam. Ibn Hazm's Fisal (Detailed Critical Examination) also stressed the importance of sense perception as he realized that human reason can be flawed, and thus criticized some of the more rationalist theologians who placed too much emphasis on reason. While he recognized the importance of reason, since the Qur'an itself invites reflection, he argued that this reflection refers mainly to sense data, since the principles of reason are themselves derived entirely from sense experience. He concludes that reason is not a faculty for independent research or discovery, but that that sense perception should be used in its place, an idea which forms the basis of empiricism.
Al-Ghazali (1058–1111) had an important influence on the use of logic in theology, as he was the first to apply the Avicennian system of temporalmodal logic to Islamic theology. He also established the application of three types of logical systems in Islamic Sharia law: reasoning by analogy, deductive logic, and inductive logic. In cases that have multiple legal precedents, he recommended the use of inductive logic, stating that the "larger the number of pieces of textual evidence is, the stronger our knowledge becomes." His followers, Fakhr al-Din al-Razi (1149-1209) and Ibn Taymiyyah (1263-1328), also applied inductive logic to Islamic Sharia law. Ibn Taymiyyah in particular argued against the certainty of syllogistic arguments and in favour of analogy.
Ibn al-Nafis (1213-1288) wrote two major works dealing with logic in Islamic theology. Theologus Autodidactus was a fictional story dealing with many Islamic topics. Through its story, Ibn al-Nafis attempted to establish that the human mind is capable of deducing the natural, philosophical and religious truths of Islam through logical thinking. In A Short Account of the Methodology of Hadith, he demonstrated the use of logic in the classification of the hadiths into four categories: decidedly true (maclūm al-sidq), probably true (yuz annu bihi'l-sidq), probably false (yuz annu bihi'l-kadhb) and decidedly false (maclūm al-kadhb).
Most early Muslim logicians during the 8th and 9th centuries produced commentaries on Aristotelian logic. The first original Arabic writings on logic were produced by al-Kindi (Alkindus) (805–873), who produced a summary on earlier logic up to his time.
Ibn Rushd (Averroes) (1126–1198) was the last major logician from al-Andalus, who wrote the most elaborate commentaries on Aristotelian logic. He was also the last major Aristotelian logician from the Islamic world. Though his commentaries on Aristotelian logic and metaphysics had little influence in the Islamic world, his commentaries had a strong influence on medieval Europe after the Latin translations of the 12th century.
The last major logician to write a commentary on Aristotelian logic was Ibn al-Nafis (1213-1288), though he himself was not an Aristotelian logician. He wrote the Al-Wurayqat (The Little Papers), a commentary on Aristotle's Organon and Rhetoric.
Al-Farabi (Alfarabi) (873–950) is considered the father of logic in the Islamic philosophical tradition. Though he was mainly an Aristotelian logician, he included a number of non-Aristotelian elements in his works. He discussed the topics of future contingents, the number and relation of the categories, the relation between logic and grammar, and non-Aristotelian forms of inference.
Al-Farabi also considered the theories of conditional syllogisms and analogical inference, which were part of the Stoic tradition of logic rather than the Aristotelian. Another addition al-Farabi made to the Aristotelian tradition was his introduction of the concept of poeticsyllogism in a commentary on Aristotle's Poetics.
Main article: Avicennian logic
Dimitri Gutas and the Stanford Encyclopedia of Philosophy consider the period between the 11th and 14th centuries to be the "Golden Age" of Arabic and Islamic philosophy, initiated by Al-Ghazali's successful integration of logic into the Madrasah curriculum and the subsequent rise of Avicennism.
Ibn Sina (Avicenna) (980–1037) developed his own system of logic known as "Avicennian logic" as an alternative to Aristotelian logic. After the Latin translations of the 12th century, Avicennian logic also influenced early medieval European logicians such as Albertus Magnus and John Duns Scotus, though Aristotelian logic later became more dominant in Europe due to the strong influence of Averroism.
The first criticisms of Aristotelian logic were written by Avicenna, who produced independent treatises on logic rather than commentaries. He criticized the logical school of Baghdad for their devotion to Aristotle at the time. He investigated the theory of definition and classification and the quantification of the predicates of categorical propositions, and developed an original theory on temporalmodalsyllogism. Its premises included modifiers such as "at all times", "at most times", and "at some time".
He wrote on the hypothetical syllogism and on the propositional calculus, which were both part of the Stoic logical tradition. He developed an original theory of “temporallymodalized” syllogistic and made use of inductive logic, such as the methods of agreement, difference and concomitant variation which are critical to the scientific method.
One of Avicenna's ideas had a particularly important influence on Western logicians such as William of Ockham. Avicenna's word for a meaning or notion (ma'na), was translated by the scholastic logicians as the Latin intentio. In medieval logic and epistemology, this is a sign in the mind that naturally represents a thing. This was crucial to the development of Ockham's conceptualism. A universal term (e.g. "man") does not signify a thing existing in reality, but rather a sign in the mind (intentio in intellectu) which represents many things in reality. Ockham cites Avicenna's commentary on Metaphysics V in support of this view.
- See also: Avicennian logic
The Islamic theologian Fakhr al-Din al-Razi (b. 1149) criticised Aristotle's "first figure" and formulated an early system of inductive logic, foreshadowing the system of inductive logic developed by John Stuart Mill (1806-1873). Al-Razi also applied inductive logic to Islamic Sharia law and Fiqh jurisprudence. Al-Razi's work was seen by later Islamic scholars as marking a new direction for Islamic logic, towards a Post-Avicennian logic. This was further elaborated by his student Afdaladdîn al-Khûnajî (d. 1249), who developed a form of logic revolving around the subject matter of conceptions and assents. In response to this tradition, Nasir al-Din al-Tusi (1201-1274) began a tradition of Neo-Avicennian logic which remained faithful to Avicenna's work and existed as an alternative to the more dominant Post-Avicennian school over the following centuries. Al-Tusi's work included the following commentary on Avicenna's theory of absolute propositions:
"What spurred him to this was that in the assertoric syllogistic Aristotle and others sometimes used contradictories of absolute propositions on the assumption that they are absolute; and that was why so many decided that absolutes did contradict absolutes. When Avicenna had shown this to be wrong, he wanted to give a way of construing those examples from Aristotle."
Systematic refutations of Greek logic were written by the Illuminationist school, founded by Shahab al-Din Suhrawardi (1155-1191), who developed the idea of "decisive necessity", which refers to the reduction of all modalities (necessity, possibility, contingency and impossibility) to the single mode of necessity.Ibn al-Nafis (1213-1288) wrote a book on Avicennian logic, which was a commentary of Avicenna's Al-Isharat (The Signs) and Al-Hidayah (The Guidance).
Najm al-Dīn al-Qazwīnī al-Kātibī (d. 1276), a student of al-Tusi, was the author of a work on logic, Al-Risāla al-Shamsiyya (Logic for Shams al-Dīn), that was commonly used as the first major text on logic in Sunnimadrasahs, right down until the 20th century and is "perhaps the most studied logic textbook of all time." Al-Qazwīnī's logic was largely inspired by the Avicenna's formal system of temporalmodal logic, but is more elaborate and departs from it in several ways. While Avicenna considered ten modalities and examined six of them, Al-Qazwlni considers many more modalized propositions and examines thirteen which he considers 'customary to investigate'.
Another systematic refutation of Greek logic was written by Ibn Taymiyyah (1263-1328), the Ar-Radd 'ala al-Mantiqiyyin (Refutation of Greek Logicians), where he argued against the usefulness, though not the validity, of the syllogism and in favour of inductive reasoning, providing a logical proof for induction being a superior form of argument, which had an important influence on the development of the scientific method of observation and experimentation. He also applied inductive logic to Islamic Sharia law and Fiqh jurisprudence. The "fundamental idea underlying Ibn Thymiyya's theory of logic in general, and legal logic in particular, is that the knowledge of the external world results from the observation of particular things." This could be seen as an anticipation of Mill's theory in the 19th century. Later, Ibn Taymiyyah argued against the certainty of syllogistic arguments and in favour of analogy. His argument is that concepts founded on induction are themselves not certain but only probable, and thus a syllogism based on such concepts is no more certain than an argument based on analogy. He further claimed that induction itself is founded on a process of analogy. His model of analogical reasoning was based on that of juridical arguments. This model of analogy has been used in the work of John F. Sowa.
In the 14th century, the Islamic sociologist and historiographer Ibn Khaldun discussed the Post-Avicennian tradition in his Muqaddimah (1377). He wrote the following on how Islamic logic had changed substantially since the 12th century:
"Treatment of [the subject as newly conceived] has become lengthy and wide-ranging—the first to do this was Fakhraddîn ar-Râzî (d. 1210) and, after him, Afdaladdîn al-Khûnajî (d. 1249), on whom Eastern scholars rely even now… The books and ways of the ancients have been abandoned, as though they had never been."
The Sharh al-takmil fi'l-mantiq written by Muhammad ibn Fayd Allah ibn Muhammad Amin al-Sharwani in the 15th century is the last major Arabic work on logic that has been studied. However, there have been "thousands and thousands of pages" devoted to logical subjects throughout the period from the 14th century through to the 19th century. Only a fraction of the texts written during this period have been studied, hence little is known about the original work on Islamic logic produced during this later period.
On the influence of Islamic mathematics on modern logic, Hermann Weyl wrote: "Occidental mathematics has in past centuries broken away from the Greek view and followed a course which seems to have originated in India and which has been transmitted, with additions, to us by the Arabs; in it the concept of number appears as logically prior to the concepts of geometry." (Weyl, 1929)
Main article: Fuzzy logic
In 1965, the Iranian Azeri mathematician Lotfi Asker Zadeh founded fuzzy set theory as an extension of the classical notion of set and he founded the field of Fuzzy Mathematics.
Later in 1973, Zadeh founded the field of Fuzzy logic. This was the first major contribution to logic from the Islamic world after more than five centuries.
The Japanese were the first to utilize fuzzy logic for practical applications. The first notable application was on the high-speed train in Sendai, in which fuzzy logic was able to improve the economy, comfort, and precision of the ride. It has also been used in recognition of hand written symbols in Sony pocket computers, Canon auto-focus technology, Omron auto-aiming cameras, earthquake prediction and modeling at the Institute of Seismology Bureau of Metrology in Japan, etc.
Major figures in Islamic logicEdit
- ↑ 1.01.11.21.31.41.5History of logic: Arabic logic, Encyclopædia Britannica.
- ↑ 2.02.1Tony Street (2000). "TOWARD A HISTORY OF SYLLOGISTIC AFTER AVICENNA: NOTES ON RESCHER'S STUDIES ON ARABIC MODAL LOGIC". Journal of Islamic Studies 11 (2): 209–228. Oxford University Press. doi:10.1093/jis/11.2.209.
- ↑ 3.03.13.23.3Goodman, Lenn Evan (2003), Islamic Humanism, p. 155, Oxford University Press, ISBN 0-19-513580-6.
- ↑ 4.04.14.24.3Muhammad Iqbal, The Reconstruction of Religious Thought in Islam, "The Spirit of Muslim Culture" (cf. and )
- ↑ 5.05.1Goodman, Lenn Evan (1992); Avicenna, p. 188, Routledge, ISBN 0-415-01929-X.
- ↑ 6.06.16.2Ruth Mas (1998). "Qiyas: A Study in Islamic Logic". Folia Orientalia 34: 113–128. ISSN0015-5675.
- ↑ 7.07.17.27.3John F. Sowa; Arun K. Majumdar (2003). "Analogical reasoning". Conceptual Structures for Knowledge Creation and Communication, Proceedings of ICCS 2003. Berlin: Springer-Verlag. http://www.jfsowa.com/pubs/analog.htm., pp. 16-36
- ↑ 8.08.1Hallaq, Wael B. (1985-1986). "The Logic of Legal Reasoning in Religious and Non-Religious Cultures: The Case of Islamic Law and the Common Law". Cleveland State Law Review 34: 79–96 [91–5].
- ↑Wael B. Hallaq (1993), Ibn Taymiyya Against the Greek Logicians, p. 48. Oxford University Press, ISBN 0198240430.
- ↑Seyyed Hossein Nasr and Oliver Leaman (1996), History of Islamic Philosophy, pp. 107-109, Routledge, ISBN 0415056675.
- ↑Ibn Hazm, Islamic Philosophy Online.
- ↑Hallaq, Wael B. (1985-1986). "The Logic of Legal Reasoning in Religious and Non-Religious Cultures: The Case of Islamic Law and the Common Law". Cleveland State Law Review 34: 79–96 [91–3].
- ↑ 13.013.113.2Dr. Abu Shadi Al-Roubi (1982), "Ibn Al-Nafis as a philosopher", Symposium on Ibn al-Nafis, Second International Conference on Islamic Medicine: Islamic Medical Organization, Kuwait (cf.Ibn al-Nafis As a Philosopher, Encyclopedia of Islamic World).
- ↑Nahyan A. G. Fancy (2006), "Pulmonary Transit and Bodily Resurrection: The Interaction of Medicine, Philosophy and Religion in the Works of Ibn al-Nafīs (d. 1288)", p. 67-73, Electronic Theses and Dissertations, University of Notre Dame.
- ↑"Mysticism in Arabic and Islamic Philosophy". Stanford Encyclopedia of Philosophy (March 7, 2009). Retrieved on 2010-04-01.
- ↑Feldman, Seymour (1964-11-26). "Rescher on Arabic Logic". The Journal of Philosophy 61 (22): 724–734. doi:10.2307/2023632. ISSN0022362X. Retrieved on 2010-03-24.</cite> . <cite class="book" style="font-style:normal" >Long, A. A.; D. N. Sedley (1987). The Hellenistic Philosophers. Vol 1: Translations of the principal sources with philosophical commentary. Cambridge: Cambridge University Press. ISBN 0-521-27556-3.</cite> </li>
- ↑<cite style="font-style:normal">Ludescher, Tanyss (February 1996). "The Islamic roots of the poetic syllogism". College Literature. Retrieved on 2008-02-29.</cite> </li>
- ↑ 18.018.118.218.3Tony Street (July 23, 2008). "Arabic and Islamic Philosophy of Language and Logic". Stanford Encyclopedia of Philosophy. Retrieved on 2008-12-05. </li>
- ↑Richard F. Washell (1973), "Logic, Language, and Albert the Great", Journal of the History of Ideas34 (3), p. 445-450 . </li>
- ↑<cite style="font-style:normal">Taneli Kukkonen (2000). "Possible Worlds in the Tahâfut al-Falâsifa: Al-Ghazâlî on Creation and Contingency". Journal of the History of Philosophy 38 (4): 479–502. doi:10.1353/hph.2005.0033.</cite> </li>
- ↑Dag Nikolaus Hasse (September 19, 2008). "Influence of Arabic and Islamic Philosophy on the Latin West". Stanford Encyclopedia of Philosophy. Retrieved on 2009-10-13. </li>
- ↑History of logic: Arabic logic, Encyclopædia Britannica. </li>
- ↑Kneale p. 229 </li>
- ↑Kneale: p. 266; Ockham: Summa Logicae i. 14; Avicenna: Avicennae Opera Venice 1508 f87rb </li>
- ↑<cite style="font-style:normal">Hallaq, Wael B. (1985-1986). "The Logic of Legal Reasoning in Religious and Non-Religious Cultures: The Case of Islamic Law and the Common Law". Cleveland State Law Review 34: 79–96 [91–2].</cite> </li>
- ↑Dr. Lotfollah Nabavi, Sohrevardi's Theory of Decisive Necessity and kripke's QSS System, Journal of Faculty of Literature and Human Sciences. </li>
- ↑"Illuminated Islamic Manuscript: A Selection of New Acquisitions at Yale University". Yale University Library, Near Eastern Collection (2009-08-06). Retrieved on 2010-03-17. </li>
- ↑Page 227 of <cite class="book" style="font-style:normal" >al-Rahim, Ahmed H. (2003). "The Twelver Si'i Reception of Avicenna in the Mongol Period", Before and After Avicenna: Proceedings of the First Conference of the Avicenna Study Group, Islamic philosophy, theology and science: texts and studies. Brill. ISBN 9789004129788
Main article: Islamic philosophy
Early Islamic philosophy or classical Islamic philosophy is a period of intense philosophical development beginning in the 2nd century AH of the Islamic calendar (early 9th century CE) and lasting until the 6th century AH (late 12th century CE). The period is known as the Islamic Golden Age, and the achievements of this period had a crucial influence in the development of modern philosophy and science; for Renaissance Europe, the influence represented “one of the largest technology transfers in world history.”. This period starts with al-Kindi in the 9th century and ends with Averroes (Ibn Rushd) at the end of 12th century. The death of Averroes effectively marks the end of a particular discipline of Islamic philosophy usually called the Peripatetic Arabic School, and philosophical activity declined significantly in Western Islamic countries, namely in Islamic Spain and North Africa, though it persisted for much longer in the Eastern countries, in particular Persia and India where several schools of philosophy continued to flourish: Avicennism, Illuminationist philosophy, Mystical philosophy, and Transcendent theosophy.
Some of the significant achievements of early Muslim philosophers included the development of a strict science of citation, the isnad or "backing"; the development of a method of open inquiry to disprove claims, the ijtihad, which could be generally applied to many types of questions (although which to apply it to is an ethical question); the willingness to both accept and challenge authority within the same process; recognition that science and philosophy are both subordinate to morality, and that moral choices are prior to any investigation or concern with either; the separation of theology (kalam) and law (shariah) during the early Abbasid period, a precursor to secularism; the distinction between religion and philosophy, marking the beginning of secular thought; the beginning of a peer review process; early ideas on evolution; the beginnings of the scientific method, an important contribution to the philosophy of science; the introduction of temporalmodal logic and inductive logic; the beginning of social philosophy, including the formulation of theories on social cohesion and social conflict; the beginning of the philosophy of history; the development of the philosophical novel and the concepts of empiricism and tabula rasa; and distinguishing between essence and existence.
Saadia Gaon, David ben Merwan al-Mukkamas, Maimonides, and Thomas Aquinas, were influenced by the Mutazilite work, particularly Avicennism and Averroism, and the Renaissance and the use of empirical methods were inspired at least in part by Arabic translations of Greek, Jewish, Persian and Egyptian works translated into Latin during the Renaissance of the 12th century, and taken during the Reconquista in 1492.
Early Islamic philosophy can be divided into clear sets of influences, branches, schools, and fields, as described below.
The life of Muhammad or sira which generated both the Qur'an (revelation) and hadith (his daily utterances and discourses on social and legal matters), during which philosophy was defined by Muslims as consisting in acceptance or rejection of his message. Together the sira and hadith constitute the sunnah and are validated by isnad ("backing") to determine the likely truth of the report of any given saying of Muhammad. Key figures are Imam Ja'far al-Sadiq, Imam Bukhari, Imam Muslim, Al-Tirmidhi, Ibn Majah, Abu Dawud and Al-Nasa'i. Each sifted through literally millions of hadith to accept a list of under 1. This work, which was not completed until the 10th century, began shortly after The Farewell Sermon in 631.
Main article: Kalam
Ilm al-Kalām (Arabic: علم الكلام, literally the study of "speech" or "words") is the Islamic philosophical discipline of seeking theological principles through dialectic. Kalām in Islamic practice relates to the discipline of seeking theological knowledge through debate and argument. A scholar of kalām is referred to as a mutakallim (plural mutakallimiin).
With Kalam, questions about the sira and hadith, as well as science (Islamic science) and law (fiqh and sharia), began to be investigated beyond the scope of Muhammad's beliefs. This period is characterized by emergence of ijtihad and the first fiqh. As the Sunnah became published and accepted, philosophy separate from Muslim theology was discouraged due to a lack of participants. During this period, traditions similar to Socratic method began to evolve, but philosophy remained subordinate to religion.
Independent minds exploiting the methods of ijtihad sought to investigate the doctrines of the Qur'an, which until then had been accepted in faith on the authority of divine revelation. One of the first debates was that between partisan of the Qadar (Arabic: qadara, to have power), who affirmed free will, and the Jabarites (jabar, force, constraint), who maintained the belief in fatalism.
At the 2nd century of the Hijra, a new movement arose in the theological school of Basra, Iraq. A pupil, Wasil ibn Ata (AD 700–748), who was expelled from the school of Hasan of Basra because his answers were contrary to then orthodox Islamic tradition and became leader of a new school, and systematized the radical opinions of preceding sects, particularly those of the Qadarites. This new school was called Mutazilite (from i'tazala, to separate oneself, to dissent) that lasted from the 8th to 10th centuries. Its principal dogmas were three:
- God is an absolute unity, and no attribute can be ascribed to Him.
- Man is a free agent. It is on account of these two principles that the Mu'tazilities designate themselves the "Partisans of Justice and Unity".
- All knowledge necessary for the salvation of man emanates from his reason; humans could acquire knowledge before, as well as after, Revelation, by the sole light of reason. This fact makes knowledge obligatory upon all men, at all times, and in all places.
The Mutazilities, compelled to defend their principles against the orthodox Islam of their day, looked for support in philosophy, and are one of the first to pursue a rational theology called Ilm-al-Kalam (Scholastic theology); those professing it were called Mutakallamin. This appellation became the common name for all seeking philosophical demonstration in confirmation of religious principles. The first Mutakallamin had to debate both the orthodox and the non-Muslims, and they may be described as occupying the middle ground between those two parties. But subsequent generations were to large extent critical towards the Mutazilite school, especially after formation of the Asharite concepts. Throughout history, the place of kalam in Islamic thought has been controversial. The vast majority of the early traditional Sunni Muslim scholars have either criticized or prohibited it. Jewish and Muslim Peripatetics, generally, stopped short in their respective Aristotelianism whenever there was danger of wounding orthodox religion.
From the 9th century onward, owing to Caliphal-Ma'mun and his successor, Greek philosophy was introduced among the Arabs, and the Peripatetic school began to find able representatives among them; such were Al-Kindi, Al-Farabi, Ibn Sina (Avicenna), and Ibn Rushd (Averroës), all of whose fundamental principles were considered as criticized by the Mutakallamin. Another trend, represented by the Brethren of Purity, used Aristotelian language to expound a fundamentally Neoplatonic and Neopythagorean world view.
During the Abbasid caliphate a number of thinkers and scientists, some of them heterodox Muslims or non-Muslims, played a role in transmitting Greek, Hindu, and other pre-Islamic knowledge to the ChristianWest. They contributed to making Aristotle known in Christian Europe. Three speculative thinkers, al-Farabi, Ibn Sina (Avicenna) and al-Kindi, combined Aristotelianism and Neoplatonism with other ideas introduced through Islam. They were considered by many as highly unorthodox and a few even described them as non-Islamic philosophers.
From Spain Arabic philosophic literature was translated into Hebrew and Latin, contributing to the development of modern European philosophy. The philosophers Moses Maimonides (a Jew born in Muslim Spain) and Ibn Khaldun (born in modern-day Tunisia), the father of sociology and historiography, were also important philosophers, though the latter did not identify himself as a falsafa, but rather a kalam author.
Some differences between Kalam and Falsafa
Aristotle attempted to demonstrate the unity of God; but from the view which he maintained, that matter was eternal, it followed that God could not be the Creator of the world. To assert that God's knowledge extends only to the general laws of the universe, and not to individual and accidental things, is tantamount to denying prophecy. One other part of Aristotle's theory shocked the faith of the Mutakallamin — the Aristotelian theory of the soul. According to Aristotelianism, the human soul is simply man's substantial form, the set of properties that make matter into a living human body. This seems to imply that the human soul cannot exist apart from the body. Indeed, Aristotle writes, "It is clear that the soul, or at least some parts of it (if it is divisible), cannot be separated from the body. [...] And thus, those have the right idea who think that the soul does not exist without the body." In Aristotelianism, at least one psychological force, the active intellect, can exist apart from the body. However, according to many interpretations, the active intellect is a superhuman entity emanating from God and enlightening the human mind, not a part of any individual human soul. Thus, Aristotle's theories seem to deny the immortality of the individual human soul.
Wherefore the Mutakallamin had, before anything else, to establish a system of philosophy to demonstrate the creation of matter, and they adopted to that end the theory of atoms as enunciated by Democritus. They taught that atoms possess neither quantity nor extension. Originally atoms were created by God, and are created now as occasion seems to require. Bodies come into existence or die, through the aggregation or the sunderance of these atoms. But this theory did not remove the objections of philosophy to a creation of matter.
For, indeed, if it be supposed that God commenced His work at a certain definite time by His "will", and for a certain definite object, it must be admitted that He was imperfect before accomplishing His will, or before attaining His object. In order to obviate this difficulty, the Motekallamin extended their theory of the atoms to Time, and claimed that just as Space is constituted of atoms and vacuum, Time, likewise, is constituted of small indivisible moments. The creation of the world once established, it was an easy matter for them to demonstrate the existence of a Creator, and that God is unique, omnipotent, and omniscient.
Main protagonists of Falsafa and their critics
The 12th century saw the apotheosis of pure philosophy and the decline of the Kalam, which later, being attacked by both the philosophers and the orthodox, perished for lack of champions. This supreme exaltation of philosophy may be attributed, in great measure, to Al-Ghazali (1005–1111) among the Persians, and to Judah ha-Levi (1140) among the Jews. It can be argued that the attacks directed against the philosophers by Al-Ghazali in his work, Tahafut al-Falasifa (The Incoherence of the Philosophers), not only produced, by reaction, a current favorable to philosophy, but induced the philosophers themselves to profit by his criticism. They thereafter made their theories clearer and their logic closer. The influence of this reaction brought forth the two greatest philosophers that the Islamic Peripatetic school ever produced, namely, Ibn Bajjah (Avempace) and Ibn Rushd (Averroes), both of whom undertook the defense of philosophy.
Since no idea and no literary or philosophical movement ever germinated on Persian or Arabian soil without leaving its impress on the Jews, the Persian Ghazali found an imitator in the person of Judah ha-Levi. This poet also took upon himself to free his religion from what he saw as the shackles of speculative philosophy, and to this end wrote the "Kuzari", in which he sought to discredit all schools of philosophy alike. He passes severe censure upon the Mutakallamin for seeking to support religion by philosophy. He says, "I consider him to have attained the highest degree of perfection who is convinced of religious truths without having scrutinized them and reasoned over them" ("Kuzari", v.). Then he reduced the chief propositions of the Mutakallamin, to prove the unity of God, to ten in number, describing them at length, and concluding in these terms: "Does the Kalam give us more information concerning God and His attributes than the prophet did?" (Ib. iii. and iv.) Aristotelianism finds no favor in Judah ha-Levi's eyes, for it is no less given to details and criticism; Neoplatonism alone suited him somewhat, owing to its appeal to his poetic temperament.
Ibn Rushd (Averroës), the contemporary of Maimonides, closed the first great philosophical era of the Muslims. He was a defender of Aristotelian philosophy against Ash'ari theologians led by Al-Ghazali. Averroes' philosophy was considered controversial in Muslim circles. The theories of Ibn Rushd do not differ fundamentally from those of Ibn Bajjah and Ibn Tufail, who only follow the teachings of Ibn Sina (Avicenna) and Al-Farabi. Like all Islamic Peripatetics, Ibn Rushd admits the hypothesis of the intelligence of the spheres and the hypothesis of universal emanation, through which motion is communicated from place to place to all parts of the universe as far as the supreme world—hypotheses which, in the mind of the Arabic philosophers, did away with the dualism involved in Aristotle's doctrine of pure energy and eternal matter. His ideas on the separation of philosophy and religion, further developed by the Averroist school of philosophy, were later influential in the development of modern secularism.
But while Al-Farabi, Ibn Sina (Avicenna), and other Persian and Muslim philosophers hurried, so to speak, over subjects that trenched on religious dogmas, Ibn Rushd delighted in dwelling upon them with full particularity and stress. Thus he says, "Not only is matter eternal, but form is potentially inherent in matter; otherwise, it were a creation ex nihilo" (Munk, "Mélanges", p. 444). According to this theory, therefore, the existence of this world is not only a possibility, as Ibn Sina declared—in order to make concessions to the orthodox— but also a necessity.
Driven from the Islamic schools, Islamic philosophy found a refuge with the Jews, to whom belongs the honor of having transmitted it to the Christian world. A series of eminent men—such as the Ibn Tibbons, Narboni, Gersonides—joined in translating the Arabic philosophical works into Hebrew and commenting upon them. The works of Ibn Rushd especially became the subject of their study, due in great measure to Maimonides, who, in a letter addressed to his pupil Joseph ben Judah, spoke in the highest terms of Ibn Rushd's commentary.
It should be mentioned that this depiction of intellectual tradition in Islamic Lands is mainly dependent upon what West could understand (or was willing to understand) from this long era. In contrast, there are some historians and philosophers who do not agree with this account and describe this era in a completely different way. Their main point of dispute is on the influence of different philosophers on Islamic Philosophy, especially the comparative importance of eastern intellectuals such as Ibn Sina and of western thinkers such as Ibn Rushd.
Main article: Judeo-Islamic philosophies (800 - 1400)
The oldest Jewish religio-philosophical work preserved is that of Saadia Gaon (892-942), Emunot ve-Deot, "The Book of Beliefs and Opinions". In this work Saadia treats the questions that interested the Mutakallamin, such as the creation of matter, the unity of God, the divine attributes, the soul, etc. Saadia criticizes other philosophers severely. For Saadia there was no problem as to creation: God created the world ex nihilo, just as the Bible attests; and he contests the theory of the Mutakallamin in reference to atoms, which theory, he declares, is just as contrary to reason and religion as the theory of the philosophers professing the eternity of matter.
To prove the unity of God, Saadia uses the demonstrations of the Mutakallamin. Only the attributes of essence (sifat al-dhatia) can be ascribed to God, but not the attributes of action (sifat-al-fi'aliya). The soul is a substance more delicate even than that of the celestial spheres. Here Saadia controverts the Mutakallamin, who considered the soul an "accident" 'arad (compare Guide for the Perplexed i. 74), and employs the following one of their premises to justify his position: "Only a substance can be the substratum of an accident" (that is, of a non-essential property of things). Saadia argues: "If the soul be an accident only, it can itself have no such accidents as wisdom, joy, love", etc. Saadia was thus in every way a supporter of the Kalam; and if at times he deviated from its doctrines, it was owing to his religious views; just as the Jewish and Muslim Peripatetics stopped short in their respective Aristotelianism whenever there was danger of wounding orthodox religion.
Main article: Al-Farabi
Al-Farabi (Alfarabi) was a founder of his own school of Islamic philosophy but which was later overshadowed by Avicennism. Al-Farabi's school of philosophy "breaks with the philosophy of Plato and Aristotle [... and ...] moves from metaphysics to methodology, a move that anticipates modernity", and "at the level of philosophy, Alfarabi unites theory and practice [... and] in the sphere of the political he liberates practice from theory". His Neoplatonic theology is also more than just metaphysics as rhetoric. In his attempt to think through the nature of a First Cause, Alfarabi discovers the limits of human knowledge".
Al-Farabi had great influence on science and philosophy for several centuries, and was widely considered second only to Aristotle in knowledge (alluded to by his title of "the Second Teacher") in his time. His work, aimed at synthesis of philosophy and Sufism, paved the way for the work of Ibn Sina (Avicenna).
Main article: Avicennism
Due to Avicenna's (Ibn Sina's) successful reconciliation between Aristotelianism and Neoplatonism along with Kalam, Avicennism eventually became the leading school of Islamic philosophy by the 12th century. Avicenna had become a central authority on philosophy by then, and several scholars in the 12th century commented on his strong influence at the time:
"People nowadays [believe] that truth is whatever [Ibn Sina] says, that it is inconceivable for him to err, and that whoever contradicts him in anything he says cannot be rational."
Avicennism was also influential in medieval Europe, particularly his doctrines on the nature of the soul and his existence-essence distinction, along with the debates and censure that they raised in scholastic Europe. This was particularly the case in Paris, where Avicennism was later proscribed in 1210. Nevertheless, his psychology and theory of knowledge influenced William of Auvergne and Albertus Magnus, and his metaphysics influenced the thought of Thomas Aquinas.
Main articles: Averroes and Averroism
Averroes (Ibn Rushd) is most famous for his commentaries on Aristotle's works and for writing The Incoherence of the Incoherence in which he defended the falasifa against al-Ghazali's The Incoherence of the Philosophers. While he had very little influence in the Islamic world, which was then dominated by Avicennian philosophy and Ash'ari theology, Averroism became very influential in medieval Europe, especially among the Scholastics. Averroism eventually led to the development of modern secularism, for which Ibn Rushd is considered as the founding father of secular thought in Western Europe.
The concept of "existence precedes essence", a key foundational concept of existentialism, can also be found in the works of Averroes, as a reaction to Avicenna's concept of "essence precedes existence".
Main article: Islamic ethics
Perhaps due to resource scarcity in most Islamic nations, there was an emphasis on limited (and some claim also sustainable) use of natural capital, i.e. producing land. Traditions of haram and hima and early urban planning were expressions of strong social obligations to stay within carrying capacity and to preserve the natural environment as an obligation of khalifa or "stewardship".
Muhammad is considered a pioneer of environmentalism for his teachings on environmental preservation. His hadiths on agriculture and environmental philosophy were compiled in the "Book of Agriculture" of the Sahih Bukhari, which included the following saying:
"There is none amongst the believers who plants a tree, or sows a seed, and then a bird, or a person, or an animal eats thereof, but it is regarded as having given a charitable gift [for which there is great recompense]."
Several such statements concerning the environment are also found in the Qur'an, such as the following:
"And there is no animal in the earth nor bird that flies with its two wings, but that they are communities like yourselves."
The earliest known treatises dealing with environmentalism and environmental science, especially pollution, were Arabic medical treatises written by al-Kindi, Qusta ibn Luqa, al-Razi, Ibn Al-Jazzar, al-Tamimi, al-Masihi, Avicenna, Ali ibn Ridwan, Ibn Jumay‘, Isaac Israeli ben Solomon, Ibn al-Quff, and Ibn al-Nafis. Their works covered a number of subjects related to pollution such as air pollution, water pollution, soil contamination, municipal solid waste mishandling, and environmental impact assessments of certain localities.Cordoba, al-Andalus also had the first waste containers and waste disposal facilities for litter collection.
Main article: Bimaristan
The ethical standards of Muslim physicians was first laid down in the 9th century by Ishaq bin Ali Rahawi, who wrote the Adab al-Tabib (Conduct of a Physician), the first treatist dedicated to medical ethics. He regarded physicians as "guardians of souls and bodies", and wrote twenty chapters on various topics related to medical ethics, including:
Many medieval Muslim thinkers pursued humanistic, rational and scientific discourses in their search for knowledge, meaning and values. A wide range of Islamic writings on love poetry, history and philosophical theology show that medieval Islamic thought was open to the humanistic ideas of individualism, occasional secularism, skepticism and liberalism.
Another reason the Islamic world flourished during the Middle Ages was an early emphasis on freedom of speech, as summarized by al-Hashimi (a cousin of Caliph al-Ma'mun) in the following letter to one of the religious opponents he was attempting to convert through reason:
"Bring forward all the arguments you wish and say whatever you please and speak your mind freely. Now that you are safe and free to say whatever you please appoint some arbitrator who will impartially judge between us and lean only towards the truth and be free from the empery of passion, and that arbitrator shall be Reason, whereby God makes us responsible for our own rewards and punishments. Herein I have dealt justly with you and have given you full security and am ready to accept whatever decision Reason may give for me or against me. For "There is no compulsion in religion" (Qur'an 2:256) and I have only invited you to accept our faith willingly and of your own accord and have pointed out the hideousness of your present belief. Peace be with you and the blessings of God!"
Certain aspects of Renaissance humanism has its roots in the medieval Islamic world, including the "art of dictation, called in Latin, ars dictaminis," and "the humanist attitude toward classical language."
Main article: Logic in Islamic philosophy
In early Islamic philosophy, logic played an important role. Islamic law placed importance on formulating standards of argument, which gave rise to a novel approach to logic in Kalam, but this approach was later displaced by ideas from Greek philosophy and Hellenistic philosophy with the rise of the Mu'tazili philosophers, who highly valued Aristotle's Organon. The works of Hellenistic-influenced Islamic philosophers were crucial in the reception of Aristotelian logic in medieval Europe, along with the commentaries on the Organon by Averroes. The works of al-Farabi, Avicenna, al-Ghazali and other Muslim logicians who often criticized and corrected Aristotelian logic and introduced their own forms of logic, also played a central role in the subsequent development of European logic during the Renaissance.
According to the Routledge Encyclopedia of Philosophy:
"For the Islamic philosophers, logic included not only the study of formal patterns of inference and their validity but also elements of the philosophy of language and even of epistemology and metaphysics. Because of territorial disputes with the Arabic grammarians, Islamic philosophers were very interested in working out the relationship between logic and language, and they devoted much discussion to the question of the subject matter and aims of logic in relation to reasoning and speech. In the area of formal logical analysis, they elaborated upon the theory of terms, propositions and syllogisms as formulated in Aristotle's Categories, De interpretatione and Prior Analytics. In the spirit of Aristotle, they believed that all rational argument can be reduced to a syllogism, and they regarded syllogistic theory as the focal point of logic. Even poetics was considered as a syllogistic art in some fashion by most of the major Islamic Aristotelians."
Important developments made by Muslim logicians included the development of "Avicennian logic" as a replacement of Aristotelian logic. Avicenna's system of logic was responsible for the introduction of hypothetical syllogism, temporalmodal logic and inductive logic. Other important developments in early Islamic philosophy include the development of a strict science of citation, the isnad or "backing", and the development of a scientific method of open inquiry to disprove claims, the ijtihad, which could be generally applied to many types of questions.
Logic in Islamic law and theology
Early forms of analogical reasoning, inductive reasoning and categorical syllogism were introduced in Fiqh (Islamic jurisprudence), Sharia (Islamic law) and Kalam (Islamic theology) from the 7th century with the process of Qiyas, before the Arabic translations of Aristotle's works. Later during the Islamic Golden Age, there was a logical debate among Islamic philosophers, logicians and theologians over whether the term Qiyas refers to analogical reasoning, inductive reasoning or categorical syllogism. Some Islamic scholars argued that Qiyas refers to inductive reasoning, which Ibn Hazm (994-1064) disagreed with, arguing that Qiyas does not refer to inductive reasoning, but refers to categorical syllogism in a real sense and analogical reasoning in a metaphorical sense. On the other hand, al-Ghazali (1058–1111) (and in modern times, Abu Muhammad Asem al-Maqdisi) argued that Qiyas refers to analogical reasoning in a real sense and categorical syllogism in a metaphorical sense. Other Islamic scholars at the time, however, argued that the term Qiyas refers to both analogical reasoning and categorical syllogism in a real sense.
The first original Arabic writings on logic were produced by al-Kindi (Alkindus) (805–873), who produced a summary on earlier logic up to his time. The first writings on logic with non-Aristotelian elements was produced by al-Farabi (Alfarabi) (873–950), who discussed the topics of future contingents, the number and relation of the categories, the relation between logic and grammar, and non-Aristotelian forms of inference. He is also credited for categorizing logic into two separate groups, the first being "idea" and the second being "proof".
Averroes (1126–98) was the last major logician from al-Andalus, who wrote the most elaborate commentaries on Aristotelian logic.
Avicenna (980-1037) developed his own system of logic known as "Avicennian logic" as an alternative to Aristotelian logic. By the 12th century, Avicennian logic had replaced Aristotelian logic as the dominant system of logic in the Islamic world.
The first criticisms of Aristotelian logic were written by Avicenna (980–1037), who produced independent treatises on logic rather than commentaries. He criticized the logical school of Baghdad for their devotion to Aristotle at the time. He investigated the theory of definition and classification and the quantification of the predicates of categorical propositions, and developed an original theory on "temporalmodal" syllogism. Its premises included modifiers such as "at all times", "at most times", and "at some time".
While Avicenna (980-1037) often relied on deductive reasoning in philosophy, he used a different approach in medicine. Ibn Sina contributed inventively to the development of inductive logic, which he used to pioneer the idea of a syndrome. In his medical writings, Avicenna was the first to describe the methods of agreement, difference and concomitant variation which are critical to inductive logic and the scientific method.
Ibn Hazm (994-1064) wrote the Scope of Logic, in which he stressed on the importance of senseperception as a source of knowledge.Al-Ghazali (Algazel) (1058–1111) had an important influence on the use of logic in theology, making use of Avicennian logic in Kalam. Despite the logical sophistication of al-Ghazali, the rise of the Ash'ari school in the 12th century slowly suffocated original work on logic in much of the Islamic world, though logic continued to be studied in some Islamic regions such as Persia and the Levant.
Fakhr al-Din al-Razi (b. 1149) criticised Aristotle's "first figure" and developed a form of inductive logic, foreshadowing the system of inductive logic developed by John Stuart Mill (1806–1873). Systematic refutations of Greek logic were written by the Illuminationist school, founded by Shahab al-Din Suhrawardi (1155–1191), who developed the idea of "decisive necessity", an important innovation in the history of logical philosophical speculation. Another systematic refutation of Greek logic was written by Ibn Taymiyyah (1263–1328), the Ar-Radd 'ala al-Mantiqiyyin (Refutation of Greek Logicians), where he argued against the usefulness, though not the validity, of the syllogism and in favour of inductive reasoning.
Main article: Islamic metaphysics
Cosmological and ontological arguments
Main article: Proof of the Truthful
Avicenna's proof for the existence of God, known as the "Proof of the Truthful", was the first ontological argument, which he proposed in the Metaphysics section of The Book of Healing. This was the first attempt at using the method of a priori proof, which utilizes intuition and reason alone. Avicenna's proof of God's existence is unique in that it can be classified as both a cosmological argument and an ontological argument. "It is ontological insofar as ‘necessary existence’ in intellect is the first basis for arguing for a Necessary Existent". The proof is also "cosmological insofar as most of it is taken up with arguing that contingent existents cannot stand alone and must end up in a Necessary Existent."
Distinction between essence and existence
Islamic philosophy, imbued as it is with Islamic theology, distinguishes more clearly than Aristotelianism the difference between essence and existence. Whereas existence is the domain of the contingent and the accidental, essence endures within a being beyond the accidental. This was first described by Avicenna's works on metaphysics, who was himself influenced by al-Farabi.
Some orientalists (or those particularly influenced by Thomist scholarship) argued that Avicenna was the first to view existence (wujud) as an accident that happens to the essence (mahiyya). However, this aspect of ontology is not the most central to the distinction that Avicenna established between essence and existence. One cannot therefore make the claim that Avicenna was the proponent of the concept of essentialismper se, given that existence (al-wujud) when thought of in terms of necessity would ontologically translate into a notion of the Necessary-Existent-due-to-Itself (wajib al-wujud bi-dhatihi), which is without description or definition, and particularly without quiddity or essence (la mahiyya lahu). Consequently, Avicenna's ontology is 'existentialist' when accounting for being qua existence in terms of necessity (wujub), while it is 'essentialist' in terms of thinking about being qua existence (wujud) in terms of contingency qua possibility (imkan; or mumkin al-wujud: contingent being).
Some argue that Avicenna anticipated Frege and Bertrand Russell in "holding that existence is an accident of accidents" and also anticipated Alexius Meinong's "view about nonexistent objects." He also provided early arguments for "a 'necessary being' as cause of all other existents."
The idea of "essence precedes existence" is a concept which dates back to Avicenna and his school of Avicennism as well as Shahab al-Din Suhrawardi and his Illuminationist philosophy. The opposite idea of "existence precedes essence" was thus developed in the works of Averroes and Mulla Sadra's transcendent theosophy.
More careful approaches are needed in terms of thinking about philosophers (and theologians) in Islam in terms of phenomenological methods of investigation in ontology (or onto-theology), or by way of comparisons that are made with Heidegger's thought and his critique of the history of metaphysics.
Ibn al-Nafis wrote the Theologus Autodidactus as a defense of "the system of Islam and the Muslims' doctrines on the missions of Prophets, the religious laws, the resurrection of the body, and the transitoriness of the world." The book presents rational arguments for bodily resurrection and the immortality of the human soul, using both demonstrative reasoning and material from the hadith corpus as forms of evidence. Later Islamic scholars viewed this work as a response to Avicenna's metaphysical argument on spiritual resurrection (as opposed to bodily resurrection), which was earlier criticized by al-Ghazali.
Soul and spirit
The Muslim physician-philosophers, Avicenna and Ibn al-Nafis, developed their own theories on the soul. They both made a distinction between the soul and the spirit, and in particular, the Avicennian doctrine on the nature of the soul was influential among the Scholastics. Some of Avicenna's views on the soul included the idea that the immortality of the soul is a consequence of its nature, and not a purpose for it to fulfill. In his theory of "The Ten Intellects", he viewed the human soul as the tenth and final intellect.
Avicenna generally supported Aristotle's idea of the soul originating from the heart, whereas Ibn al-Nafis on the other hand rejected this idea and instead argued that the soul "is related to the entirety and not to one or a few organs." He further criticized Aristotle's idea that every unique soul requires the existence of a unique source, in this case the heart. Ibn al-Nafis concluded that "the soul is related primarily neither to the spirit nor to any organ, but rather to the entire matter whose temperament is prepared to receive that soul" and he defined the soul as nothing other than "what a human indicates by saying ‘I’."
- Further information: Avicennism - Thought experiments on self-consciousness
While he was imprisoned in the castle of Fardajan near Hamadhan, Avicenna wrote his famous "Floating Man" thought experiment to demonstrate human self-awareness and the substantiality of the soul. He referred to the living human intelligence, particularly the active intellect, which he believed to be the hypostasis by which God communicates truth to the human mind and imparts order and intelligibility to nature. His "Floating Man" thought experiment tells its readers to imagine themselves suspended in the air, isolated from all sensations, which includes no sensory contact with even their own bodies. He argues that, in this scenario, one would still have self-consciousness. He thus concludes that the idea of the self is not logically dependent on any physical thing, and that the soul should not be seen in relative terms, but as a primary given, a substance.
This argument was later refined and simplified by René Descartes in epistemic terms when he stated: "I can abstract from the supposition of all external things, but not from the supposition of my own consciousness."
In contrast to ancient Greek philosophers who believed that the universe had an infinite past with no beginning, medieval philosophers and theologians developed the concept of the universe having a finite past with a beginning. This view was inspired by the creation myth shared by the three Abrahamic religions: Judaism, Christianity and Islam. The Christian philosopher, John Philoponus, presented the first such argument against the ancient Greek notion of an infinite past. However, the most sophisticated medieval arguments against an infinite past were developed by the Islamic philosopher, Al-Kindi (Alkindus); the Jewish philosopher, Saadia Gaon (Saadia ben Joseph); and the Islamic theologian, Al-Ghazali (Algazel). They developed two logical arguments against an infinite past, the first being the "argument from the impossibility of the existence of an actual infinite", which states:
- "An actual infinite cannot exist."
- "An infinite temporal regress of events is an actual infinite."
- "∴ An infinite temporal regress of events cannot exist."
The second argument, the "argument from the impossibility of completing an actual infinite by successive addition", states:
- "An actual infinite cannot be completed by successive addition."
- "The temporal series of past events has been completed by successive addition."
- "∴ The temporal series of past events cannot be an actual infinite."
Both arguments were adopted by later Christian philosophers and theologians, and the second argument in particular became more famous after it was adopted by Immanuel Kant in his thesis of the first antimony concerning time.
In metaphysics, Avicenna (Ibn Sina) defined truth as:
"What corresponds in the mind to what is outside it."
Avicenna elaborated on his definition of truth in his Metaphysics:
"The truth of a thing is the property of the being of each thing which has been established in it."
In his Quodlibeta, Thomas Aquinas wrote a commentary on Avicenna's definition of truth in his Metaphysics and explained it as follows:
"The truth of each thing, as Avicenna says in his Metaphysica, is nothing else than the property of its being which has been established in it. So that is called true gold which has properly the being of gold and attains to the established determinations of the nature of gold. Now, each thing has properly being in some nature because it stands under the complete form proper to that nature, whereby being and species in that nature is."