This paper will offer a systematic reconstruction of al-Ġazālī’s Sceptical Argument in his celebrated Deliverer/Delivered from Going Astray (al-Munqiḏ/al-Munqaḏ min al-Ḍalāl). Based on textual evidence, I will argue that the concept of certainty (yaqīn) in play in this argument is that of the philosophers—most notably Ibn Sīnā—and that it is firmly tied to demonstration (burhān) and hence to the materials of syllogism (mawwād al-qiyās). This will show that contrary to what many scholars believe, this Sceptical Argument is al-Ġazālī’s discovery of (...) a latent sceptical problem in Muslim philosophers’ epistemological theories based on Aristotle’s Posterior Analytics that escaped even the agile mind of aš-šayḫ ar-raʾīs Ibn Sīnā. This reconstruction will also shed some light on the widespread assumption that al-Ġazālī anticipates Descartes’s sceptical considerations in the First Meditation. I will argue that not only do the two thinkers use incompatible strategies to reach their respective sceptical conclusions, but both their conclusions and their use of God in refuting them are also essentially non-identical. The conclusion is that the two sceptical arguments are essentially different. (shrink)