Astrology: The discussion of the human soul, its existence, nature, ultimate objective and eternity, occupies a highly important position in Islamic philosophy and forms its main focus. For the most part Muslim philosophers agreed, as did their Greek predecessors, that the soul consists of non-rational and rational parts. The non-rational part they divided into the plant and animal souls, the rational part into the practical and the theoretical intellects.
All believed that the non-rational part is linked essentially to the body, but some considered the rational part as separate from the body by nature and others that all the parts of the soul are by nature material. The philosophers agreed that, while the soul is in the body, its non-rational part is to manage the body, its practical intellect is to manage worldly affairs, including those of the body, and its theoretical intellect is to know the eternal aspects of the universe.
THE EXISTENCE OF THE SOUL
All Muslim philosophers concerned themselves with the subject of the soul. We infer the existence of the soul from the fact that we observe bodies that perform certain acts with some degree of will. These acts are exemplified in taking nourishment, growing, reproducing, moving and perceiving. Since these acts do not belong to the nature of bodies, for this nature is devoid of will, they must belong to a principle they have other than bodies. This principle is what is called ‘soul’. This argument is intended to prove the existence of the animal soul, which includes the plant soul.
THE NATURE OF THE SOUL
While Islam made it incumbent on Muslim philosophers to occupy themselves extensively with the study of the soul and to make certain statements that in some cases appear consistent with Islamic beliefs, Greek philosophy had the upper hand in forming the real convictions of Muslim philosophers with regard to the nature of the soul. Unless otherwise specified, reference to: he soul here is limited to the terrestrial soul to the exclusion of the celestial one, since Muslim philosophers concerned themselves primarily with the former.
THE RATIONAL SOUL
The rational soul, which is defined as a primary perfection for an organic natural body inasmuch as this body can act by rational choice and grasp the universals, is divided into the practical and the theoretical intellects. The practical intellect seeks knowledge in order to act in accordance with the good in its individual body, its family and its state. It must, therefore, know the principles for properly managing the body, the family and the state, that is, ethics, home management and politics. The practical intellect is the rational soul turning its face downward. The function of the theoretical intellect is to know just for the sake of having the universals. Some of these natures, such as God and the intellect, cannot attach to movement; knowledge of them is metaphysics. Other natures, such as unity, can attach to movement but do not; knowledge of them is mathematics.
THE ULTIMATE OBJECTIVE OF THE SOUL
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.