 Avicenna strongly criticises this doctrine (Avicenna 1996, III: 292–93; Avicenna 1959: 239–40). One thing cannot become another substantially, nor can a rational soul unite with the Active Intellect which is indivisible. The human intellect cannot be united with intelligibilia. Rather one knows things by conjunction (ittisal) not union (ittihad) with the Active Intellect from whence one grasps the universals of things immanent in it. The soul receives the forms from the Active intellect but remains unchanged itself. The forms inhere in the soul-intellect through the material intellect. Avicenna criticises Porphyry for popularising the fallacy of union and change. But in doing so Avicenna marks a sharp distinction between God’s knowledge and human knowledge. According to Mulla Sadra, one cannot hold such a view about God’s knowledge because it violates both His unity and the fact of His knowledge of particulars.