The soul is treated as a collection of faculties (kowa) or forces acting on the body: all activity of any sort, in bodies animal or vegetable, as well as human, proceeds either from such forces added to the body or from the mixture of elements from which the body is formed. The simplest soul condition is that of the vegetable whose activity is limited to nutrition and generation and accretion by growth (Najat, p. 43). The animal soul possesses the vegetable faculties but adds to them others, and the human soul adds yet others to these, and the addition made to the human soul enables it to be described as a rational soul. The faculties present in the soul may be divided into two classes, the faculties of perception and the faculties of action. The faculties of perception are partly external and partly internal: of these the external faculties exist in the body wherein the soul dwells and are the eight senses, sight, hearing, taste, smell, perception of heat and cold, perception of dry and moist, perception of resistance as by hard and soft, and perception of rough and smooth. By means of these senses the form of the external object is reproduced in the soul of the percipient. There are four internal faculties of perception: (i.) al-musawira, “the formative,” whereby the soul perceives the object without the aid of the senses as by an act of imagination; (ii.) al-mufakkira, “the cogitative,” by which the soul perceiving a number of qualities associated together abstracts one or more of them from the others with which they are associated, or groups together those which are not seen as connected; this is the faculty of abstraction which is employed in forming general ideas; (iii.) al wahm, or “opinion,” by means of which a general conclusion is drawn from a number of ideas grouped together; and (iv.) al-hafiza or az-zakira, “memory,” which preserves and records the judgments formed. Men and animals perceive particulars by means of sense; man attains the knowledge of universals by means of reason. The `aql or rational soul of man is conscious of its own faculties, not by means of an external, i.e., bodily sense, but immediately by the exercise of its own reasoning power. This proves to be an independent entity, even though accidentally connected with a body and dependent on that body for sense perception: the possibility of direct knowledge without sense perception shows that it is not essentially dependent on the body, and the possibility of its existence without the body, which follows logically from its independence, is the proof of its immortality. Every living creature perceives that it has only one ego or soul in itself, and this soul, says Ibn Sina, did not exist prior to the body but was created, that is to say, proceeded by emanation from the Agent Intellect at the time when the body was generated. (Najat, p. 51).
Under the head of Physics Ibn Sina considers the forces observed in nature, including all that are in the soul, save only that which is peculiar to the rational soul of man. These forces are of three kinds: some, such as weight, are an essential part of the body in which they occur; others are external to the body on which they act, and are such as cause movement or rest; and others, again, are such as the faculties possessed by the non-rational souls of the spheres, which produce movement directly without external impulse. No force is infinite; it may be increased or diminished, and always produces a finite result.
Time is regarded as essentially dependent on movement; although it is not itself a form of movement, so far as the idea of time is concerned, it is measured and made known by the movements of the heavenly bodies. Following al-Kindi place is defined as “the limit of the container which touches the contained.” Vacuum is “only a name”, in fact it is impossible, for all space can be increased, diminished, or divided into parts, and so must contain something capable of increase, etc.
God alone is “necessary being,” and so the supreme reality. Space, time, etc., belong to “actual being,” and whatever necessity they possess is derived from God. The objects studied in physical science are only “possible being,” which may or may not become “actual being.” God alone is necessarily existent through all eternity: He is the truth in the sense that He alone is true absolutely, all other reality is so only in so far as it is derived from God. From God by emanation comes the `aql or “Agent Intellect,” and from this proceeds the intellect or reason which differentiates the rational soul in man from the soul in other creatures. To every man this intellect is given, and in due course it returns to the “Agent Intellect” which was its source. The soul’s possible activity, independent of the body with which it is associated, proves its immortality, but this immortality does not imply separate existence, but rather reabsorption in the source. From the `aql also proceeds the universe, but not like the reason of man by direct emanation, but by the medium of successive emanations.
Ibn Sina was the last of the great philosophers of the East. Two causes combined to terminate philosophy proper in Asiatic Islam. In the first place it had become closely identified with the Shi`ite heresies, and was thus in bad repute in the eyes of the orthodox; whilst the Shi`ite sects themselves, all of the extremer kind (ghulat), which had devoted themselves most to philosophical studies, had also taken up a number of pre-Islamic religious theories, such as transmigration of souls, etc., which were detrimental to scientific research. Neo-Platonism had shown itself at an earlier period prone to similar tendencies. As a result the Shi`ites tended towards mystic and often fantastic theories, which were discouraging to the study of Aristotelian doctrines. The second cause lay in the rise of dominant Turkish elements, Mahmud of Ghazna, then the Saljuk Turks, which were of uncompromising orthodoxy, and abhorred everything which was associated with the Shi`ites or tended to rationalism. For all that it left permanent marks in Asiatic Islam in two directions: in orthodox scholasticism and in mysticism.
We have already noted that Muslim b. Muhammad Abu l-Qasim al-Majriti al-Andalusi (d. 395-6), as his name denotes, a native of Madrid, brought the teachings of the Brethren of Purity to Spain, and so incidentally aroused an interest there in the philosophy which had been studied in the East. For some time no important results appeared, then followed a series of brilliant philosophical writers and teachers, deriving their inspiration partly from the Brethren, and partly from the Jewish students.