Metaphysics and cosmology
In contrast to al-Kindi, who considered the subject of metaphysics to be God, al-Farabi believed that it was concerned primarily with being qua being (that is, being in and of itself), and this is related to God only to the extent that God is a principle of absolute being. Al-Kindi's view was, however, a common misconception regarding Greek philosophy amongst Muslim intellectuals at the time, and it was for this reason that Avicenna remarked that he did not understand Aristotle's Metaphysics properly until he had read a prolegomenon written by al-Farabi.
Al-Farabi's cosmology is essentially based upon three pillars: Aristotelian metaphysics of causation, highly developed Plotinian emanational cosmology and the Ptolemaic astronomy. In his model, the universe is viewed as a number of concentric circles; the outermost sphere or "first heaven", the sphere of fixed stars, Saturn, Jupiter, Mars, the Sun, Venus, Mercury and finally, the Moon. At the centre of these concentric circles is the sub-lunar realm which contains the material world. Each of these circles represent the domain of the secondary intelligences (symbolized by the celestial bodies themselves), which act as causal intermediaries between the First Cause (in this case, God) and the material world. Furthermore these are said to have emanated from God, who is both their formal and efficient cause.
The process of emanation begins (metaphysically, not temporally) with the First Cause, whose principal activity is self-contemplation. And it is this intellectual activity that underlies its role in the creation of the universe. The First Cause, by thinking of itself, "overflows" and the incorporeal entity of the second intellect "emanates" from it. Like its predecessor, the second intellect also thinks about itself, and thereby brings its celestial sphere (in this case, the sphere of fixed stars) into being, but in addition to this it must also contemplate upon the First Cause, and this causes the "emanation" of the next intellect. The cascade of emanation continues until it reaches the tenth intellect, beneath which is the material world. And as each intellect must contemplate both itself and an increasing number of predecessors, each succeeding level of existence becomes more and more complex. It should be noted that this process is based upon necessity as opposed to will. In other words, God does not have a choice whether or not to create the universe, but by virtue of His own existence, He causes it to be. This view also suggests that the universe is eternal, and both of these points were criticized by al-Ghazzali in his attack on the philosophers
In his discussion of the First Cause (or God), al-Farabi relies heavily on negative theology. He says that it cannot be known by intellectual means, such as dialectical division or definition, because the terms used in these processes to define a thing constitute its substance. Therefore if one was to define the First Cause, each of the terms used would actually constitute a part of its substance and therefore behave as a cause for its existence, which is impossible as the First Cause is uncaused; it exists without being caused. Equally, he says it cannot be known according to genus and differentia, as its substance and existence are different from all others, and therefore it has no category to which it belongs. If this were the case, then it would not be the First Cause, because something would be prior in existence to it, which is also impossible. This would suggest that the more philosophically simple a thing is, the more perfect it is. And based on this observation, Adamson says it is possible to see the entire hierarchy of al-Farabi's cosmology according to classification into genus and species. Each succeeding level in this structure has as its principal qualities multiplicity and deficiency, and it is this ever-increasing complexity that typifies the material world.
Epistemology and eschatology
Human beings are unique in al-Farabi's vision of the universe because they stand between two worlds: the "higher", immaterial world of the celestial intellects and universal intelligibles, and the "lower", material world of generation and decay; they inhabit a physical body, and so belong to the "lower" world, but they also have a rational capacity, which connects them to the "higher" realm. Each level of existence in al-Farabi's cosmology is characterized by its movement towards perfection, which is to become like the First Cause; a perfect intellect. Human perfection (or "happiness"), then, is equated with constant intellection and contemplation.
Al-Farabi divides intellect into four categories: potential, actual, acquired and the Agent. The first three are the different states of the human intellect and the fourth is the Tenth Intellect (the moon) in his emanational cosmology. The potential intellect represents the capacity to think, which is shared by all human beings, and the actual intellect is an intellect engaged in the act of thinking. By thinking, al-Farabi means abstracting universal intelligibles from the sensory forms of objects which have been apprehended and retained in the individual's imagination.
This motion from potentiality to actuality requires the Agent Intellect to act upon the retained sensory forms; just as the Sun illuminates the physical world to allow us to see, the Agent Intellect illuminates the world of intelligibles to allow us to think. This illumination removes all accident (such as time, place, quality) and physicality from them, converting them into primary intelligibles, which are logical principles such as "the whole is greater than the part". The human intellect, by its act of intellection, passes from potentiality to actuality, and as it gradually comprehends these intelligibles, it is identified with them (as according to Aristotle, by knowing something, the intellect becomes like it). Because the Agent Intellect knows all of the intelligibles, this means that when the human intellect knows all of them, it becomes associated with the Agent Intellect's perfection and is known as the acquired Intellect.
While this process seems mechanical, leaving little room for human choice or volition, Reisman says that al-Farabi is committed to human voluntarism. This takes place when man, based on the knowledge he has acquired, decides whether to direct himself towards virtuous or unvirtuous activities, and thereby decides whether or not to seek true happiness. And it is by choosing what is ethical and contemplating about what constitutes the nature of ethics, that the actual intellect can become "like" the active intellect, thereby attaining perfection. It is only by this process that a human soul may survive death, and live on in the afterlife.
According to al-Farabi, the afterlife is not the personal experience commonly conceived of by religious traditions such as Islam and Christianity. Any individual or distinguishing features of the soul are annihilated after the death of the body; only the rational faculty survives (and then, only if it has attained perfection), which becomes one with all other rational souls within the agent intellect and enters a realm of pure intelligence. Henry Corbin compares this eschatology with that of the Ismaili Neo-Platonists, for whom this process initiated the next grand cycle of the universe. However, Deborah Black mentions we have cause to be skeptical as to whether this was the mature and developed view of al-Farabi, as later thinkers such as Ibn Tufayl, Averroes and Ibn Bajjah would assert that he repudiated this view in his commentary on the Nicomachean Ethics, which has been lost to modern experts.
Psychology, the soul and prophetic knowledge
In his treatment of the human soul, al-Farabi draws on a basic Aristotelian outline, which is informed by the commentaries of later Greek thinkers. He says it is composed of four faculties: The appetitive (the desire for, or aversion to an object of sense), the sensitive (the perception by the senses of corporeal substances), the imaginative (the faculty which retains images of sensible objects after they have been perceived, and then separates and combines them for a number of ends), and the rational, which is the faculty of intellection. It is the last of these which is unique to human beings and distinguishes them from plants and animals. It is also the only part of the soul to survive the death of the body. Noticeably absent from these scheme are internal senses, such as common sense, which would be discussed by later philosophers such as Avicenna and Averroes.
Special attention must be given to al-Farabi's treatment of the soul's imaginative faculty, which is essential to his interpretation of prophethood and prophetic knowledge. In addition to its ability to retain and manipulate sensible images of objects, he gives the imagination the function of imitation. By this he means the capacity to represent an object with an image other than its own. In other words, to imitate "x" is to imagine "x" by associating it with sensible qualities that do not describe its own appearance. This extends the representative ability of the imagination beyond sensible forms and to include temperaments, emotions, desires and even immaterial intelligibles or abstract universals, as happens when, for example, one associates "evil" with "darkness". The prophet, in addition to his own intellectual capacity, has a very strong imaginative faculty, which allows him to receive an overflow of intelligibles from the agent intellect (the tenth intellect in the emanational cosmology). These intelligibles are then associated with symbols and images, which allow him to communicate abstract truths in a way that can be understood by ordinary people. Therefore what makes prophetic knowledge unique is not its content, which is also accessible to philosophers through demonstration and intellection, but rather the form that it is given by the prophet's imagination.
Practical philosophy (ethics and politics)
The practical application of philosophy is a major concern expressed by al-Farabi in many of his works, and while the majority of his philosophical output has been influenced by Aristotelian thought, his practical philosophy is unmistakably based on that of Plato. In a similar manner to Plato's Republic, al-Farabi emphasizes that philosophy is both a theoretical and practical discipline; labeling those philosophers who do not apply their erudition to practical pursuits as "futile philosophers". The ideal society, he says, is one directed towards the realization of "true happiness" (which can be taken to mean philosophical enlightenment) and as such, the ideal philosopher must hone all the necessary arts of rhetoric and poetics to communicate abstract truths to the ordinary people, as well as having achieved enlightenment himself. Al-Farabi compares the philosopher's role in relation to society with a physician in relation to the body; the body's health is affected by the "balance of its humours" just as the city is determined by the moral habits of its people. The philosopher's duty, he says, is to establish a "virtuous" society by healing the souls of the people, establishing justice and guiding them towards "true happiness".
Of course, al-Farabi realizes that such a society is rare and requires a very specific set of historical circumstances to be realized, which means very few societies could ever attain this goal. He divides those "vicious" societies, which have fallen short of the ideal "virtuous" society, into three categories: ignorant, wicked and errant. Ignorant societies have, for whatever reason, failed to comprehend the purpose of human existence, and have supplanted the pursuit of happiness for another (inferior) goal, whether this be wealth, sensual gratification or power. It is interesting to note that democratic societies also fall into this category, as they too lack any guiding principle. Both wicked and errant societies have understood the true human end, but they have failed to follow it. The former because they have willfully abandoned it, and the latter because their leaders have deceived and misguided them. Al-Farabi also makes mention of "weeds" in the virtuous society; those people who try to undermine its progress towards the true human end. The best known Arabic source for al-Farabi's political philosophy is his work titled, al-Madina al-fadila (The Virtuous City).
Whether or not al-Farabi actually intended to outline a political programme in his writings remains a matter of dispute amongst academics. Henry Corbin, who considers al-Farabi to be a crypto-Shi'ite, says that his ideas should be understood as a "prophetic philosophy" instead of being interpreted politically. On the other hand, Charles Butterworth contends that nowhere in his work does al-Farabi speak of a prophet-legislator or revelation (even the word philosophy is scarcely mentioned), and the main discussion that takes place concerns the positions of "king" and "statesmen". Occupying a middle position is David Reisman, who like Corbin believes that al-Farabi did not want to expound a political doctrine (although he does not go so far to attribute it to Islamic Gnosticism either). He argues that al-Farabi was using different types of society as examples, in the context of an ethical discussion, to show what effect correct or incorrect thinking could have. Lastly, Joshua Parens argues that al-Farabi was slyly asserting that a pan-Islamic society could not be made, by using reason to show how many conditions (such as moral and deliberative virtue) would have to be met, thus leading the reader to conclude that humans are not fit for such a society. Some other authors like Mykhaylo Yakubovych attest that for al-Farabi religion (milla) and philosophy (falsafa) constituted the same praxeological value (i.e. basis for amal al-fadhil—"virtuous deed"), while its epistemological level (ilm—"knowledge") was different.