In the ‘first’ and ‘second’ proofs of the eighteenth discussion of his Tahafut al- Falasifa, Abu Hamid al-Ghazali (1058-1111) raises objections against Ibn Sina’s arguments for the immateriality of the soul. Both proofs turn on the premise that a relation between a divisible (material) substratum and an indivisible object of cognition (the intelligible form) is impossible. Ghazali’s objection, that this proposition is inconsistent with ibn Sina’s theory of perception, and the role therein of the wahm (‘estimative faculty’) is sound. However, this just leaves open the option of resolving the contradiction by modifying the theory of perception to make it coherent with the proof, and Ghazali does not take an explicit position on which side to take. His aim, as he says, is just to show the contradictions in the theories of the philosophers, and not to make positive positions. I will show, however, that underlying this explicit dimension of the discussion, there is a tacit philosophical point which Ghazali intends to indicate for the discerning reader. This is that the real mystery which imposes itself on a theory of the soul is not just the question of how a relation is possible between a divisible, material cognitive faculty and an indivisible object. Rather, it is the more fundamental question of the possibility of any relation between a unity and a multiplicity. This question imposes itself with equal force not only on the theory of an immaterial soul, but also on the kalam theory of a material ‘atomic’ soul. These first sections of the eighteenth discussion are therefore connected to an over-arching theme of the Tahafut in that they call attention to an apparent metaphysical impossibility which is nevertheless a manifest reality.