Man has a soul and physical body, each of which is subject to its own pleasures and diseases. What harms the body is sickness, and that which gives it pleasure lies in its well-being, health and whatever is in harmony with its nature. The science that deals with the health and the maladies of the body is the science of medicine.
The diseases of the soul constitute evil habits and submission to lusts that degrade man doom to the level of beasts. The pleasures of the 'soul are moral and ethical virtues which elevate man and move him closer to perfection and wisdom bringing him close to God. The study that deals with such matters is the science of ethics ('ilm al-akhlaq).
Before we commence a discussion of the main topics of our subject, we must prove that the soul of man is incorporeal, possesses an existence independent of the body, and is immaterial. In order to prove this, a number of arguments have been set forth amongst which we can mention the following:
1. One of the characteristics of bodies is that whenever new forms and shapes are imposed upon them, they renounce and abandon their previous forms or shapes. In the human soul, however, new forms, whether of the sensible or of the intellectual nature, enter continuously without wiping out the previously existing forms. In fact, the more impressions and intellectual forms enter the mind, the stronger does the soul become.
2. When three elements of colour, smell, and taste, appear in an object, it is transformed. The human soul however, perceives all of these conditions without being materially affected by them.
3. The pleasures that man experiences from intellectual cognition can belong only to the soul, since man's body plays no role in it.
4. Abstract forms and concepts which are perceived by the mind, are undoubtedly non-material and indivisible. Accordingly, their vehicle, which is the soul, must also be indivisible, and therefore immaterial.
5. The physical faculties of man receive their input through the senses, while the human soul perceives certain things without the help of the senses. Among the things that the human soul comprehends without relying on the senses, are the law of contradiction, the idea that the whole is always greater than one of its parts, and other such universal principles.
The negation of the errors made by the senses on the part of the soul, such as optical illusions, is done with the aid of these abstract concepts, even though the raw material required for making corrections is provided by the senses.
Now that the independent existence of the soul has been proved, let us see what are the things responsible for its well-being and delight, and what are the things that make it sick and unhappy. The health and perfection of the soul lies in its grasp of the real nature of things , and this understanding can liberate it from the narrow prison of lust and greed and all other fetters which inhibit its evolution and edification towards that ultimate stage of human perfection which lies in man's nearness to God. This is the goal of `speculative wisdom' (al-hikmat al-nadariyyah).
At the same time, the human soul must purge itself of any evil habits and traits it may have, and replace them with ethical and virtuous modes of thought and conduct. This is the goal of `practical wisdom' (al-hikmat al-`amaliyyah). Speculative and practical wisdom are related like matter and form; they cannot exist without each other.
As a matter of principle, the term "philosophy" refers to `speculative wisdom' and "ethics" refers to `.practical wisdom'. A man who has mastered both speculative wisdom and practical wisdom is a microcosmic mirror of the larger universe: the macrocosm.