Islamic philosophy developed largely out of a dialogue with classical Greek philosophy, with the work of Aristotle (384–322 BC), Plato (c.427–347 BC), and the neoplatonist Alexandrian philosopher Plotinus (AD 204/5–70) being key sources. In fact, it was largely through the Islamic tradition, and the work of Averroes (Ibn Rushd; 1126–98) in particular, that the work of such philosophers was kept alive after the break-up of the Roman Empire.  The Orthodox Byzantine empire, ruled from Constantinople, had turned its back on Greek philosophy – the Emperor Justinian closing the famous School of Athens in AD 529 – because of its pagan heritage.

When a reaction to Aristotelianism set in after the first few centuries of Islamic culture it brought in its wake a measure of scepticism, with philosophy as a discipline itself coming to be called into question by some thinkers. One such prominent anti-Aristotelian was the eleventh-century philosopher Al-Ghazali (or Algazali; 1058–1111), who was noted for exhibiting sceptical leanings at several points in his career, although he ended up as a mystic, turning to Sufism. He is described by the commentators Arthur Hyman and James J. Walsh as someone who ‘had a skeptical streak within his nature, sampled a number of theological and philosophic positions, and left an autobiographical record of his spiritual quests’. The work in which his scepticism is most evident, as well as his anti-philosophical bent, is The Incoherence of the Philosophers (written between 1091 and 1095). From our point of view it is unfortunate that Al-Ghazali’s scepticism ultimately was overcome by his religious belief. Whereas for Pyrrhonians dogmatism was the ‘disease’ to be feared, for Al-Ghazali that was scepticism. He speaks of God having ‘cured me of this malady’ in his autobiographical work Deliverance from Error (c.1100), after a prolonged period in which he felt himself to be ‘a sceptic in fact though not in theory nor in outward expression’.  Al-Ghazali then goes on to denounce philosophy in the same work, dismissing the claims of the various schools on the grounds that ‘unbelief affects them all’, and that their influence on Muslims is ‘baneful and mischievous’.

It is a claim that many in the Muslim world would uphold still today. But at least we can see the seed of scepticism present there within the Islamic tradition, and it is fascinating to observe the dialectic between scepticism and theology unfolding in this context – as it was later to do in Descartes, another philosopher for whom God was in some sense the ‘cure’ for his intellectual  ‘malady’. When that scepticism is directed against philosophy it fits into the tradition of Western scepticism, and there are similarities to be noted between Al-Ghazali and Hume on the subject of causality. Both philosophers deny any necessary connection between cause and effect, although with Al-Ghazali there is a theological aspect in God being the only source of causes in the universe. There can even be ‘causeless’ effects in Al-Ghazali’s scheme; as Hyman and Walsh note, it is a consequence of Al-Ghazali’s conception of divine omnipotence that, ‘God is able to produce any effect without any intermediate cause at all.’ Al-Ghazali is also thought to have influenced the fourteenth-century French philosopher Nicholas (sometimes spelled Nicolaus) of Autrecourt, who has been dubbed ‘the medieval Hume’, so he genuinely has a role to play in the Western as well as the Islamic tradition.

In The Incoherence of the Philosophers Al-Ghazali systematically works his way through twenty philosophical doctrines to prove that they are inconsistent with the Koran. In each case he offers a detailed refutation, and although his position is theologically based – Koranic doctrines are taken as given and felt to require no proof – he argues his case, in the words of some recent commentators, ‘with great philosophical acuity’. The doctrines in question can be traced back to Greek philosophy, and in Al-Ghazali’s reading they have come to infect Islamic philosophy with heretical notions. He speaks disparagingly of a group of thinkers, such as Alfarabi (c.870–950) and Avicenna (980–1037), who ‘have entirely cast off the reins of religion through multifarious beliefs’. ‘The source of their unbelief’, Al-Ghazali goes on to argue, ‘is their hearing high-sounding names such as “Socrates [469–399 BC],” “Hippocrates [c.460–377 BC],” “Plato,” “Aristotle,” and their likes’. The author’s appointed task is ‘to show the incoherence of their belief’ in such matters as the nature of the universe, God’s attributes, the uniformity of nature, and the nature of the soul.38 What all the philosophers being attacked have in common, in Al-Ghazali’s opinion, is that they underestimate God’s power. Some have argued for an eternal universe, whereas for the devout it is necessary to accept that it was created in an act of will by an omnipotent God. God also had the power to alter the course of nature if he chose, meaning that belief in nature’s uniformity was tantamount to heresy, as was any denial of bodily resurrection after death.

Al-Ghazali’s attack on the Aristotelian tradition in Islamic philosophy is damning, and as one of his translators has noted, ‘[i]t brought to a head the conflict between Islamic speculative theology and philosophy’. Averroes responded with a work entitled The Incoherence of the Incoherence, but Al-Ghazali’s theology-led approach exerts a considerable appeal within Islam. If one puts the theological bias to one side, however, one has some very powerful arguments against metaphysical claims. Difficult though it may be to ignore the theology, it is still worth emphasising sceptical attitudes wherever one finds them within the Islamic system.

If Al-Ghazali’s encounter with philosophy was decided in favour of religion, then the dialogue with Greek classical philosophy within Islam prompted several thinkers of the same period to start questioning the claims of religion instead. Ibn al-Rawandi (c.910?), for example, rejected the concept of prophethood and even queried the authority of the Koran: ‘even if we grant that he [Mohammed] exceeds all the Arabs in eloquence, what compelling force will this have where Persians, who do not understand the [Arabic] tongue are concerned, and what probative evidence can he advance?’ Philosophy-inspired free thought led to such iconoclastic sentiments as those expressed by the poet Abul-Ala al-Maarri (973–1057) on religious strife in the Islamic territories:

Each party defends its own religion I wonder in vain where the truth lies!

Abu Isa al-Warraq (active early eighth century) argued that neither Christianity nor Judaism could be considered to have any validity because many of their doctrines broke the rules of Aristotelian logic (al-Warraq himself was accused of Zoroastrian leanings by his Islamic contemporaries). Even if, as Majid Fakhry has noted, most theologians, like Al-Ghazali, ultimately ‘reacted violently’ against the impact of Greek philosophy on their culture, scepticism was capable of making its presence felt in the Islamic world none the less.

Scepticism is always going to be in a dialectic with theology in Islam, but that dialectic needs to be given as much encouragement as it can, such that it can be seen as intrinsic to that cultural tradition rather than a Western imposition signalling yet another round of colonial imperialism. At the very least the potential for scepticism is present in every culture. Doubt is a universal phenomenon, one that creeps into everyone’s mind at some point or other, and we can draw hope from that. Regardless of whether it is conceived of as disease or cure it is something to build upon.