AL-FARABI asserts that even though the soul is of different parts, it is a unity with all its parts working for one final end, happiness. While the plant soul, for example, serves a specific function, it also serves the powers that are higher than it in rank, the animal powers. Without nourishment, growth and reproduction, the animal powers cannot perform their necessary functions. Similarly, while the function of the animal powers is to have sensation and movement, by performing this function they also promote the functions of the powers above them, the rational ones. The operations of the animal powers, especially those of the senses, are particularly important for the attainment of the final end. The external senses strip the forms from material objects and convey them to the internal senses. The more they are transferred internally, the less mixed with matter do they become. Since the innermost sense they reach is the imagination, they are there in their purest material existence (see IMAGINATION).
The role of the objects of the imagination is not always clearly defined in Islamic philosophy. Occasionally it is said by somebody like Ibn Sina to be one of preparation for the theoretical intellect to receive the universals from the agent intellect. At other times Ibn Sina, like other Aristotelians such as Ibn Rushd, takes these objects to be the ingredients out of which the universals are made after the last process of purification (see EPISTEMOLOGY IN ISLAMIC PHILOSOPHY). It seems, however, that in either case the light of the agent intellect is needed to complete the process. In the former case, this light gives the intelligible forms to the theoretical intellect when this intellect is prepared. In the latter case, it sheds itself on the objects of the imagination, which are then reflected on the theoretical intellect without their matter. Since the theoretical intellect is in its first stages in potentiality, it cannot act on the objects of the imagination directly; hence the need for the agent intellect, which is pure actuality. The role of the practical intellect in all this is to put order into the body. This sets free the theoretical intellect from preoccupation with the body and helps the powers whose function is necessary for theoretical knowledge to function unhampered.Muslim philosophers adhered to the view that the acquired intellect is one with its objects, for they thought the knower and the known are one, as did their Greek predecessors. This means that the highest human state is one in which unity with the universals or the eternal aspects of the universe is reached. This state is described as happiness because in it eternity, an aspect of the objects of the acquired intellect, is attained.