QuestionsCan we be certain of anything?Doubt and the light
Can we be certain of anything?What escapes words

Doubt and the light

Al-Ghazali 1058 · 1111Reason has limits: certainty comes from experiencing God.
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What it claims

Certainty did not return through a proof, but through a light that God cast into the breast. First truths are not demonstrated: they are given.

Why

If reason can be doubted, no proof can rescue it; certainty that returns without proof must be a gift from God.

In short

"Doubt and the light" is an argument by Al-Ghazali (Deliverance from Error (al-Munqidh), c. 1106-1109) on the question "Can we be certain of anything?" (answer: what escapes words). Its claim: Certainty did not return through a proof, but through a light that God cast into the breast. First truths are not demonstrated: they are given. According to AskPhilosophy's logic check (Z3 solver), the argument is valid only if one grants a premise the author leaves unstated (P5). AskPhilosophy presents 3 objections, 0 of them with a documented reply, and the original text behind each premise, checked word for word.

Deliverance from Error (al-Munqidh), c. 1106-1109
Valid with an implicit premise

As a young man, al-Ghazali noticed that the children of Christians become Christians, those of Jews Jews, those of Muslims Muslims. He wanted a certainty that did not come from habit. So he put everything in doubt: the senses, then reason itself. For two months, he says, he was a sceptic "in fact, if not in words". He came out of it, but not through reasoning: through a light that God, he says, cast into his breast. This account is often compared to Descartes' doubt (dreams, deceiving senses), written five centuries later; no influence is proven, and the two men do not leave doubt in the same way.

P1The senses deceive us: the eye sees a star the size of a coin, while geometry shows it is larger than the Earth. It is reason that corrects the senses.
P2Then nothing guarantees that reason itself will not be overruled by a higher judge, as it overrules the senses. Dreams show this: while dreaming, we are sure of false things. Even the first truths of reason become doubtful.
P3Such doubt can only be removed by a proof. But every proof is built from first truths: if they are in doubt, no proof is possible.
P4Yet, after two months, confidence in the first truths of reason came back, with security and certainty.
P5 · implicit premiseA certainty that returns without proof can only come from a gift of God, and not simply from human nature or habit.
Therefore certainty did not return through a proof, but through a light that God cast into the breast. First truths are not demonstrated: they are given.

click a premise to reject it

If you accept every premise, logic forces you to accept the conclusion. So the debate is about the premises.
Checked by a logic solver: the premises cannot all be true while the conclusion is false.
Without the implicit premise: Without P5, the computer finds a case where confidence returns without proof, but without divine light: for example because our nature prevents us from doubting for long. The second half of the conclusion no longer follows.
P1 to P4 are enough to conclude that certainty did not return through a proof: this is the heart of the account, and it is valid. But to conclude that it came from a divine light, we must add P5: there would be only two possible sources, proof or God. Al-Ghazali does not defend this point; he lives it. P5 is what Hume disputes: for him, nature is enough to restore our confidence.
Analogy. To check a ruler you need another ruler. But if you doubt every ruler, you have nothing left to measure with: you cannot get out of doubt by measuring. A ruler must simply be given to you. Al-Ghazali says, moreover, that first truths are not to be sought: they are already there, and by seeking them we lose sight of them.

Objections

3

Each objection is a conversation: click to see who replies and where the debate stands.

Descartes 1637 · attacks premise 3

One can get out of doubt through reason. Even if I am dreaming, even if everything deceives me, one truth holds: I think, therefore I am. It is so firm that the most extravagant suppositions of the sceptics cannot shake it. Doubt itself provides a first fixed point, from which one can rebuild.

no reply
No reply possible: objection raised in 1637, after the author's death (1111).
The debate goes on (our summary) A comparison, not an influence: nothing proves that Descartes read al-Ghazali, and no European translation of the Munqidh is known before the 19th century. And Descartes meets the same difficulty as al-Ghazali: to go further than "I am", he relies on God, guarantor of clear ideas. Arnauld then objects that he is going in a circle (the "Cartesian circle").
Hume 1748 · attacks premise 5

No divine light is needed to get out of radical doubt. Nature is always too strong for principle: the most determined sceptic regains his beliefs as soon as he has to act. Our confidence in reason and the senses comes from our nature, not from a proof or a miracle.

no reply
No reply possible: objection raised in 1748, after the author's death (1111).
The debate goes on (our summary) Al-Ghazali could answer that it is God who gave us this nature: in the Incoherence he already says that God creates knowledge in us through habit. But then the light is no longer different from ordinary nature, and the account loses its character of an exceptional experience. The debate is about what "God's light" means.
Averroes 1179 · attacks the conclusion

The Sufi path, waiting for illumination after purifying the soul, is not a method of knowledge for everyone. If it were the path intended for humans, reasoning would be useless; yet the Qur'an constantly calls us to reflect and judge. He only grants that mastering one's desires is a condition for thinking well, as health is a condition for learning, but that it does not by itself give knowledge.

no reply
No reply possible: objection raised in 1179, after the author's death (1111).
The debate goes on (our summary) Al-Ghazali does not reject reasoning: the light precisely restores his confidence in the truths of reason, from which proofs become possible again. He himself writes that first truths should not be sought, since they are present. But he does place above reason a "taste" reserved for those who follow the Sufi path: that is the point Averroes rejects.