Al-Ghazali
Reason has limits: certainty comes from experiencing God.
Al-Ghazali (1058 – 1111, Persia and Iraq (Seljuk empire): Tus, Nishapur, Baghdad; then Damascus and Jerusalem) : islamic rational theology (kalam). Al-Ghazali studied the philosophers of his day (Avicenna, al-Farabi) well enough to summarise them, then attacked them with their own weapons in The Incoherence of the Philosophers: on twenty points, he says, they do not demonstrate what they claim. His most famous blow targets causation: we see the fire and the burning together, never the necessary link that would join them. On AskPhilosophy: 4 reconstructed arguments, 5 quotes checked word for word against the original texts, and 4 common beliefs examined; every text carries an authenticity badge (written by the author, posthumous, student notes, reported, apocryphal).
Why he matters
He is called "the proof of Islam" (Hujjat al-Islam): one of the most widely read thinkers of the Muslim world. His Incoherence of the Philosophers provoked, seventy years later, Averroes' reply. His critique of causation is often compared to Hume's, his account of doubt to Descartes', with no proven influence. And his proof from the beginning of the world was revived in the 20th century as the "kalam argument".
His times
Born in Tus, Persia, he studied in Nishapur with the great theologian al-Juwayni. In 1091 the vizier Nizam al-Mulk appointed him professor at the Nizamiyya of Baghdad, the most prestigious school of the Seljuk empire. In 1095, at the height of his fame, he went through a crisis: his tongue seized up and he could no longer teach. He left everything, lived some ten years in retreat (Damascus, Jerusalem, pilgrimage to Mecca), then returned to teach in Nishapur around 1106. He died in Tus in 1111.
Reading his books with care
In the Incoherence, he warns that he argues "as an opponent, not as the defender of a doctrine": he borrows the views of any school to refute the philosophers, without always saying what he himself thinks. His positive doctrine is in al-Iqtisad. And Deliverance from Error is an autobiography written fifteen years after the crisis: a reconstructed account, not a diary.
His positions
click a row to see the evidenceAn Ash'arite Muslim theologian. In al-Iqtisad he proves God's existence from the beginning of the world, and holds that God creates through a will that chooses.
Neither empiricist nor rationalist in the modern sense. Once his crisis was over, he trusted the senses and the first truths of reason. But above them he places knowledge by "tasting" (dhawq), that of the Sufis, and prophecy, "beyond intellect".
He demands a certainty that leaves no possible doubt. He went through radical doubt for two months, then regained confidence in first truths, "with security and certainty".
Man is made of a body and a "heart": the real nature of his spirit, the seat of the knowledge of God, not the flesh. But in the Incoherence (discussion 18) he argues that the philosophers do not demonstrate, by reason alone, that the soul is an immaterial substance.
Ash'arite: God creates everything, including our acts and the very power we have to act; man only "acquires" (kasb) his acts. Everything that happens, even evil and sin, is willed by God. Scholars debate how much room this leaves for freedom.
Nothing is obligatory through reason alone: the good and the obligatory come from the revealed Law. So values do not depend on us, but they rest on God's command, not on the nature of things.
He reasons like a logician and judges it a crime to reject mathematics in the name of religion. But reason has limits: "beyond intellect" there is prophecy, and the lived experience of the Sufis.
The goal of life is the bliss of the world to come, reached only through fear of God and by turning the soul away from its desires.
Everyone is born with a sound nature (fitra), which upbringing and imitation of parents cover over. But the soul is pulled by its desires and must be treated like a sick body.
Order and unity first: even a ruler who prevails by force must be obeyed, if he has the required qualities, to avoid civil strife.
An ethics of divine law: obligation comes from the revealed Law, not from reason or from weighing consequences. Purifying the heart (Sufism) is its practice.