 Kilwardby insists at great length on denying any efficient causality to the object, that is, he refuses to take perceptual acts as being caused by the external object or its species. The object is the necessary occasion and the causa sine qua non (otherwise there would be nothing to be perceived) but not the sufficient cause of perception (DSF 103; 123). The efficient cause per se of perception is the immaterial soul—the division into sensory faculties is instrumental to the process and in most of this part of the treatise Kilwardby talks of the operations of the sensory soul (which he also calls the ‘incorporeal sensitive spirit’) as a unified entity.