Muslim philosophers agree that knowledge is possible. Knowledge is the intellect's grasp of the immaterial forms, the pure essences or universals that constitute the natures of things, and human happiness is achieved only through the intellect's grasp of such universals. They stress that for knowledge of the immaterial forms, the human intellect generally relies on the senses. Some philosophers, such as Ibn Rushd and occasionally Ibn Sina, assert that it is the material forms themselves, which the senses provide, that are grasped by the intellect after being stripped of their materiality with the help of the divine world. However, the general view as expressed by al-Farabi and Ibn Sina seems to be that the material forms only prepare the way for the reception of the immaterial forms, which are then provided by the divine world. They also state that on rare occasions the divine world simply bestows the immaterial forms on the human intellect without any help from the senses. This occurrence is known as prophecy. While all Muslim philosophers agree that grasping eternal entities ensures happiness, they differ as to whether such grasping is also necessary for eternal existence.
Muslim philosophers are primarily concerned with human happiness and its attainment. Regardless of what they consider this happiness to be, all agree that the only way to attain it is through knowledge. The theory of knowledge, epistemology, has therefore been their main preoccupation and appears chiefly in their logical and psychological writings. Epistemology concerns itself primarily with the possibility, nature and sources of knowledge. Taking the possibility of knowledge for granted, Muslim philosophers focused their epistemological effort on the study of the nature and sources of knowledge. Their intellectual inquiries, beginning with logic and ending with metaphysics and in some cases mysticism, were in the main directed towards helping to understand what knowledge is and how it comes about.
Following in the footsteps of the Greek philosophers, Muslim philosophers consider knowledge to be the grasping of the immaterial forms, natures, essences or realities of things. They are agreed that the forms of things are either material (that is, existing in matter) or immaterial (existing in themselves). While the latter can be known as such, the former cannot be known unless first detached from their materiality. Once in the mind, the pure forms act as the pillars of knowledge. The mind constructs objects from these forms, and with these objects it makes judgments. Thus Muslim philosophers, like Aristotle before them, divided knowledge in the human mind into conception (tasawwur), apprehension of an object with no judgment, and assent (tasdiq), apprehension of an object with a judgment, the latter being, according to them, a mental relation of correspondence between the concept and the object for which it stands. Conceptions are the main pillars of assent; without conception, one cannot have a judgment. In itself, conception is not subject to truth and falsity, but assent is. However, it should be pointed out that tasdiq is a misleading term in Islamic philosophy. It is generally used in the sense of 'accepting truth or falsity', but also occasionally in the sense of 'accepting truth'. One must keep in mind, however, that when assent is said to be a form of knowledge, the word is then used, not in the broad sense to mean true or false judgment, but in the narrow sense to mean true judgment.
In Islamic philosophy, conceptions are in the main divided into the known and the unknown. The former are grasped by the mind actually, the latter potentially. Known conceptions are either self-evident (that is, objects known to normal human minds with immediacy such as 'being', 'thing' and 'necessary') or acquired (that is, objects known through mediation, such as 'triangle'). With the exception of the self-evident conceptions, conceptions are known or unknown relative to individual minds. Similarly, Muslim philosophers divided assent into the known and the unknown, and the known assent into the self-evident and the acquired. The self-evident assent is exemplified by 'the whole is greater than the part', and the acquired by 'the world is composite'. In Kitab at-tanbih 'ala sabil as-sa'ada (The Book of Remarks Concerning the Path of Happiness), al-Farabi calls the self-evident objects: 'the customary, primary, well-known knowledge, which one may deny with one's tongue, but which one cannot deny with one's mind since it is impossible to think their contrary'. Of the objects of conception and assent, only the unknown ones are subject to inquiry. By reducing the number of unknown objects one can increase knowledge and provide the chance for happiness. But how does such reduction come about?
In Islamic philosophy there are two theories about the manner in which the number of unknown objects is reduced. One theory stresses that this reduction is brought about by moving from known objects to unknown ones, the other that it is merely the result of direct illumination given by the divine world. The former is the upward or philosophical way, the second the downward or prophetic one. According to the former theory, movement from the known objects of conception to the unknown ones can be effected chiefly through the explanatory phrase (al-qawl ash-sharih). The proof (al-burhan) is the method for moving from the known objects of assent to the unknown ones. The explanatory phrase and proof can be either valid or invalid: the former leads to certitude, the latter to falsehood. The validity and invalidity of the explanatory phrase and proof can be determined by logic, which is a set of rules for such determination. Ibn Sina points out that logic is a necessary key to knowledge and cannot be replaced except by God's guidance, as opposed to other types of rules such as grammar for discourse (which can be replaced by a good natural mind) and metre for poetry (which can be replaced by good taste).
By distinguishing the valid from the invalid explanatory phrase and proof, logic serves a higher purpose, namely that of disclosing the natures or essences of things. It does this because conceptions reflect the realities or natures of things and are the cornerstones of the explanatory phrase and proof. Because logic deals only with expressions that correspond to conceptions, when it distinguishes the valid from the invalid it distinguishes at the same time the realities or natures of things from their opposites. Thus logic is described as the key to the knowledge of the natures of things. This knowledge is described as the key to happiness; hence the special status of logic in Islamic philosophy.
We are told that because logic deals only with the known and unknown, it cannot deal with anything outside the mind. Because it is a linguistic instrument (foreign in nature to the realities of things), it cannot deal with such realities directly, whether they exist in the mind or outside it, or are external to these two realms of existence. It can only deal with the states or accidents of such realities, these states comprising links among the realities and intermediaries between the realities and language. Logic therefore deals with the states of such realities, as they exist in the mind. Such states are exemplified by 'subject' or 'predicate', 'universality' or 'particularity', 'essentiality' or 'accidentality'. In other words, logic can deal with realities only in that these realities are subjects or predicates, universal or particular, essential or accidental and so on.
Because the ultimate human objective is the understanding of the realities, essences or natures of things, and because the ultimate logical objective is the understanding of conceptions, logicians must focus on the understanding of those conceptions that lead to the understanding of the essences if they intend to serve humanity. Ibn Sina points out that since the essences are universal, such expressions are also universal in the sense of representing universal conceptions such as 'human being', not in the sense of being universal only in expression, such as 'Zayd'. A universal expression can be applied to more than one thing, as the last two examples show, but one must keep in mind Ibn Sina's distinction between these two types of universal expressions: the former represents reality, although indirectly, the latter does not. It is only the former with which the logician should be concerned (see Logic in Islamic philosophy).
Considering that the discussion of universals occupies a central place in Arabic logic, it is important to focus briefly on this subject to ensure understanding of the proper objects of the knowledge of the natures of things. Muslim philosophers divide universal expressions into five types, known together as the five predicables: genus, species, difference, property and common accident. Genus refers to the common nature of all the species that fall under it, such as 'animality' for 'human being', 'dog', 'cat' and so on. As such, it tells us what the general nature of a thing is. Species refers to the common nature of all the individuals that fall under it, such as 'human being' for 'John', 'George' and 'Dorothy'. As such, it tells us what the specific nature of a thing is. Difference refers to that which differentiates the members of the genus, such as 'rational', which differentiates the species of being human from other animal species; it tells us which thing a being is. These three universals are essential to a thing; that is, without them the essence will not be what it is. Property and common accident are accidental, in that they attach to the thing but are not part of its essence. Property refers to something that necessarily attaches to one universal only, such as 'capacity for laughter' for 'human being'. Common accident refers to a quality that attaches to more than one universal, either in an inseparable manner, such as 'black' for 'crow', or in a separable manner, such as 'black' for 'human being'. The inseparability of the common accident, however, is only in existence.
Only the first three of the above universals constitute the essences of things. If one is to understand the essence of a thing, one must first understand its genus, species and difference or differences. The understanding of these three universals takes place through the explanatory phrase and proof, of which these universals are simple elements. The explanatory phrase is either definition or description. The definition is a phrase which mirrors the essence of a thing by indicating its general and specific essential qualities, that is, its genus, species and difference; the description is like the definition except that it indicates the property instead of the difference. Thus the description does not give a complete picture of the essence of a thing as does the definition. The proof is a set of propositions, which consist of conceptions joined or separated by particles. The proof that helps in the understanding of the essences of things is that which moves from known universal judgments to an unknown universal one.
The important question that concerned Muslim philosophers is how the universals or forms that are essential to the natures of things arrive at the human mind before it has the chance to employ the explanatory phrase and proof to compose known conceptions and known judgments from them. In order to answer this question, Muslim philosophers first discussed the structure of the human soul and then the steps through which the universals pass on their way to the place of knowledge (see Soul in Islamic philosophy). As stated above, conceptions come to the mind through either the philosophical way or the prophetic way. The philosophical way requires one first to use one's external senses to grasp the universals as they exist in the external world, mixed with matter. Then the internal senses, which like the external senses are a part of the animal soul, take in these universals and purify them of matter as much as possible. The imagination is the highest internal sense, in which these universals settle until the next cognitive move. It is from this point to the next step in the philosophical journey that the details seem particularly unclear.
All Muslim philosophers believe that above the senses there is the rational soul. This has two parts: the practical and theoretical intellects. The theoretical intellect is responsible for knowledge; the practical intellect concerns itself only with the proper management of the body through apprehension of particular things so that it can do the good and avoid the bad. All the major Muslim philosophers, beginning with al-Kindi, wrote treatises on the nature and function of the theoretical intellect, which may be referred to as the house of knowledge.
In addition to the senses and the theoretical intellect, Muslim philosophers include in their discussion of the instruments of knowledge a third factor. They teach that the divine world contains, among other things, intelligences, the lowest of which is what al-Kindi calls the First Intellect (al-'aql al-awwal), better known in Arabic philosophy as the 'agent intellect' (al-'aql al-fa''al), the name given to it by al-Farabi (§3), or 'the giver of forms' (wahib as-suwar). They contend that the world around us is necessary for the attainment of philosophical knowledge. Some, such as Ibn Bajja, Ibn Rushd and occasionally Ibn Sina, say that the mixed universals in the imagination that have been derived from the outside world through the senses are eventually purified completely by the light of the agent intellect, and are then reflected onto the theoretical intellect.
Al-Farabi's and Ibn Sina's general view, however, is that these imagined universals only prepare the theoretical intellect for the reception of the universals from the agent intellect that already contains them. When expressing this view, Ibn Sina states that it is not the universals in the imagination themselves that are transmitted to the theoretical intellect but their shadow, which is created when the light of the agent intellect is shed on these universals. This is similar, he says, to the shadow of an object which is reflected on the eye when sunlight is cast on that object. While the manner in which the universals in the imagination can prepare the theoretical intellect for knowledge is in general unclear, it is vaguely remarked by al-Farabi and Ibn Sina that this preparation is due to the similarity of these universals to the pure universals, and to the familiarity of the theoretical intellect with the imagined universals owing to its proximity to the imagination. In other words, the familiarity of this intellect with what resembles its proper objects prepares it for the reception of these objects from the agent intellect.
The prophetic way is a much easier and simpler path (see Prophecy). One need not take any action to receive the divinely given universals; the only requirement seems to be the possession of a strong soul capable of receiving them. While the philosophical way moves from the imagination upward to the theoretical intellect, the prophetic way takes the reverse path, from the theoretical intellect to the imagination. For this reason, knowledge of philosophy is knowledge of the natures of things themselves, while knowledge of prophecy is knowledge of the natures of things as wrapped up in symbols, the shadows of the imagination.
Philosophical and prophetic truth is the same, but it is attained and expressed differently. Ibn Tufayl's Hayy Ibn Yaqzan is the best illustration of the harmony of philosophy and religion (see Ibn Tufayl). The so-called double truth theory wrongly views these two paths to knowledge as two types of truth, thus attributing to Ibn Rushd a view foreign to Islamic philosophy. One of the most important contributions of Islamic philosophy is the attempt to reconcile Greek philosophy and Islam by accepting the philosophical and prophetic paths as leading to the same truth.
Muslim philosophers agree that knowledge in the theoretical intellect passes through stages. It moves from potentiality to actuality and from actuality to reflection on actuality, thus giving the theoretical intellect the respective names of potential intellect, actual intellect and acquired intellect. Some Muslim philosophers explain that the last is called 'acquired' because its knowledge comes to it from the outside, and so it can be said to acquire it. The acquired intellect is the highest human achievement, a holy state that conjoins the human and the divine realms by conjoining the theoretical and agent intellects.
Following in the footsteps of Alexander of Aphrodisias, al-Farabi, Ibn Bajja and Ibn Rushd believe that the theoretical intellect is potential by nature, and therefore disintegrates unless it grasps the eternal objects, the essential universals, for the known and the knower are one. Ibn Sina rejects the view that the theoretical intellect is potential by nature. He argues instead that it is eternal by nature because unless it is, it cannot grasp the eternal objects. For him, happiness is achieved by this intellect's grasping of the eternal objects, for such grasping perfects the soul. Muslim philosophers who believe that eternity is attained only through knowledge also agree with Ibn Sina that knowledge is perfection and perfection is happiness.
See also: Epistemology; Ethics in Islamic philosophy; al-Farabi (§3); Ibn Bajja (§3); Ibn Rushd (§6); Ibn Sina (§3); al-Kindi; Logic in Islamic philosophy; Meaning in Islamic philosophySHAMS C. INATI