Among the inner faculties of the soul, the faculty of illusion and imagination has a significant function in Islamic epistemology, especially Sadra's. In terms of Sadra, the mechanism of imagination is sometimes the preservation of forms, and sometimes it perceives them. Resolving this inconsistency is only possible through resorting to certain principles of Sadra. This faculty has epistemically general functions such as the preservation of forms, the transformation of the Presential knowledge to the Acquired knowledge, the visualization and representation, the retrieval and reidentification, and the specific functions such as effects in dream, revelation and inspiration, and intuition. unlike the predecessors, Sadr-ol-Mote'allehin does not consider the faculty of illusion as an independent one, but believes that intellect as descending, accompanying the faculty of sensibility, holds a relation with its properties based on which we might obtain the illusion particulars or physical attributes.

Understanding the partial meanings, creating fallacies, and affecting the basis of knowledge, is of the functions of the faculty of illusion in the realm of Islamic epistemology.

Keywords: illusion (faculty), imagination (faculty), epistemic function, epistemology, Mulla Sadra.