Sharp philosophical discussions renter on human knowledge, and these discussions occupy a central position in philosophy, especially in modern philosophy. Knowledge is the starring point of philosophical advance toward establishing a solid philosophy of the universe and this world. As long as the sources of human thought, its criteria and its values, are undetermined, it will not be possible to carry on any study, regardless of its kind.
One of the above-mentioned wide discussions is that which handles the sources and primary origins of knowledge through investigations, studies and attempts to discover the primary principles of the powerful intellectual structure with which the human race is endowed. Thus, it responds to the following questions: 'How did human beings come to know? How was their intellectual life formed, including all the thoughts and notions it possesses? And what is the source that provides them with this stream of thought and knowledge?'
Every human being knows numerous things in his life, and numerous forms of thought and knowledge are expressed in his soul. There is no doubt that many kinds of human knowledge grow out of each other. Thus, in forming new knowledge, a human being is assisted by previous knowledge. The issue is to be able to put our finger on the primary threads of thought and on the common source of knowledge in general.
To begin with, we must know that in the main, perception is divided into two kinds. One of them is conception.  This is simple knowledge.  The ether is assent. (p. 58) This is knowledge involving a judgement.  Conception is exemplified in our grasp  of the idea of heat, light or sound. Assent, on the other hand, is exemplified in our judgement  that heat is a power derived from the sun, that the sun is more luminous than the moon, and that the atom is susceptible to explosion. 
We begin now with a study of human conceptions, concentrating on their sources and causes. After that, we will take up assent and knowledge.
Conception and Its Primary Source
By the term 'primary', we mean the real source of simple conceptions or simple knowledge. The human mind contains two kinds of conceptions. One of them is simple conceptual ideas, such as the ideas of 'existence', 'unity', 'heat', 'whiteness', and similar single human conceptions. The other is composite ideas, which are the conceptions that result from a combination of simple conceptions. Thus, you may conceive 'a mountain of soil', and then conceive 'a piece of gold'. After that, you combine these two conceptions. Thus, deriving from this combination a third conception which is (p. 59) 'a mountain of gold'. This third conception is in reality composed of the previous two conceptions; hence, all composite conceptions are reduced to simple conceptual units.
The issue under consideration is the attempt to know the real source of these units and the cause of the arising of these simple conceptions in human knowledge. This issue has an important history in the various stages of Greek, Islamic and European philosophy. Throughout the history of philosophy, it received a number of solutions. These solutions can be summarized in the following theories.
I - The Platonic Theory of Recollection
This theory states that knowledge is a function of the recollection of previous information.  Plato was the founder of this theory. He based it on his specific philosophy of the archetypes.  He believed that the soul has a prior existence. Thus, he believed that prior to the existence of the body, the human soul had existed independently of the body. Since the soul's existence was completely free from matter and its restrictions, it was possible for it to be in touch with the archetypes - that is with the realities that are free from matter. Thus, it was also possible for is to know them. However, when it became necessary for the soul to descend from its immaterial world in order to be conjoined to the body and linked to it in the world of matter, this caused it to lose all its knowledge of the archetypes and fixed realities, and to forget them completely. But the soul can begin to retrieve its knowledge by means of the sense perception of specific ideas and particular things. This is because all such ideas and things are shadows and reflections of those eternal archetypes and realities that are everlasting in the world in which the soul had lived. When is perceives a specific idea, it immediately moves to the ideal reality that it had known before it became attached to the body. On this basis, our knowledge of the universal human being -that is, the universal idea of a human being - would be nothing but a recollection of an abstract reality that we had forgotten. Indeed, we remember it only due to our sense perception of this or that specific human being (p. 60) who reflects that abstract reality in the material world. Thus, universal conceptions are prior to sense perception. And perception is not realized except through the process of retrieving and recollecting such universal conceptions. Rational knowledge is not related to particular things in the sensible realm. Rather, it is only related to those abstract universal realities.
This theory is based on two philosophical propositions. One of them is that the soul exists prior to the existence of the body in a world higher than matter. The other is that rational knowledge is nothing but knowledge of the fixed abstract realities in that higher world - the Platonic technical term for these realities being 'archetypes'.
Both propositions are false, as was pointed out by critics of Plato's philosophy. For the soul, in the rational philosophical sense, is not something that exists in an abstract form and prior to the existence of the body. Rather, it is the result of a substantial movement in matter. The soul begins with this movement as material, characterized by material qualities and subjugated to the laws of matter. By means of this movement and process of completion, it acquires an immaterial existence not characterized by material qualities and not subject to the laws of matter, even though it is subject to the general laws of existence. This philosophical notion of the soul is the only one that can explain the [present] issue, and give a reasonable clarification of the relation between the soul and matter or the soul and the body. As for the Platonic notion, which supposes that the soul has an existence prior to that of the body, it is most incapable of explaining this relation, of justifying the link that exists between the soul and the body, and of clarifying the circumstances under which the soul falls from its own level to that of matter.
Besides, it is possible to explain rational knowledge - with the notion of the archetypes put aside in the field of discussion - (p. 61) by the explanation given in Aristotle's philosophy: namely, that the sensible ideas are the same as the universal ideas that the mind knows after is abstracts them from the proper qualities of individuals, and retains the common idea. The universal human being chat we know is not an ideal reality that we had previously seen in a higher world. Rather, he is the form of this or that human being, after it has been subjected to the process of abstraction by means of which the universal idea is extracted from it. (p. 62)
11 - The Rational Theory
This theory was adopted by a number of prominent European philosophers, such as Descartes,  Kant  and others. It can be summarized in the belief that there are two sources of conceptions. One of them is sense perception. Thus, we conceive 'heat', 'light', 'taste' or 'sound' due to our sense perception of all of that. The other is the innate nature. This is to say that the human mind possesses ideas and conceptions that are not derived from the senses, but are fixed in the innermost being of the innate nature. Thus, the soul draws [certain ideas] from itself. According to Descartes, these innate conceptions are the ideas of Cod, the soul, extension and movement, as well as the ideas that resemble them, and are characterized by complete clarity in the human mind. And, according to Kant, the whole field of conceptual human knowledge and science - including the two forms of time and space, as well as the twelve categories,  for which Kant is known - is innate.
The senses are, on the basis of this theory, the source of understanding the simple conceptions and ideas. However, they are not the only source. Rather, there is also the innate nature that produces in the mind a number of conceptions.
What obliged the rationalists to adopt this theory for explaining human conceptions was this. They did not find a reason for the arising of a number of ideas and conceptions from the senses, since they are non-sensible ideas. Thus, they must be derived essentially from the innermost being of the soul. This makes it clear that the philosophical motive for postulating the rational theory would be completely eliminated if we could explain the mental conceptions solidly, and without need of supposing innate ideas. Because of this, we can refute the rational theory in two ways.
The first is by analyzing knowledge in a way that would attribute all of it to the senses, and facilitate understanding the manner in which all conceptions are produced from the senses. Such an analysis would deny any justification to the theory of innate ideas, since it was based on the complete separation of some ideas from the sphere of the senses. Therefore, if it were possible to extend the reach of the senses to the various areas of conception, there would be no need for innate conceptions. This way was adopted by John Locke  in responding to Descartes and other such rationalists. Later, it was also adopted by those who upheld the empirical principle, such as Berkeley  and David Hume. 
The second way is the philosophical method for responding to [the view of] innate conceptions. It is based on the principle that a multiplicity of effects cannot be the result of chat which is simple, by virtue of the fact of its simplicity. The soul is simple. Therefore, it cannot be a cause in a natural manner of a number of conceptions and ideas. Rather, the existence of such a large number of pieces of knowledge in the soul must be caused by many external factors. These factors are the instrumental senses and the various sensations that occur to them.  (p. 68)
A complete criticism of this proof requires that we explain the principle on which it is based, and give a clarification of the reality and simplicity of the soul. But for this, there is no room here. However, we must point out the following. First, this proof - if one can accept it - does not totally demolish the theory of innate ideas, because it only demonstrates the lack of a multiplicity of innate pieces of knowledge, but does not prove that the soul does not naturally possess a limited [number of] conceptions  concordant with its unity and simplicity, and resulting in a number of other conceptions independent of the senses. In the second place, we would like to clarify that if the rational theory means that in the human soul there are innate ideas in actuality, then it becomes possible for the proof presented above to respond to this theory as follows. The soul is simple in essence; so, how could it produce that large number of innate ideas? Indeed, if the rationalists were truly inclined to believe that, then our human inner feeling would be sufficient for rejecting their theory. This is because all of us know that at the moment human beings [begin] to exist on the face of the earth, they do not possess any idea, regardless of how clear and general it is in the human mind:
God brought you out of your mothers' abdomens when you did not know anything. He gave you hearing, vision and hearts, in the hope that you will be grateful. 
Still, another interpretation of the rational theory can be recapitulated in the consideration that innate ideas exist in the soul potentially, and that they acquire the quality of being actual by the development and mental integration of the soul. Thus, innate conceptions are not produced by the senses. Rather, the soul contains them without attending to them. However, with the integration of the soul, these conceptions become knowledge, attended to and clear, as is the case of the knowledge and information that we recollect and, hence, reawaken once again after they had been latent and potential. (p. 64)
In light of this interpretation, the rational theory cannot be rejected on the basis of the philosophical demonstration or scientific evidence which has already been mentioned.
III - The Empirical Theory
This theory states that only sense perception supplies the human mind with conceptions and ideas, and that mental power is that which reflects in the mind the various sense perceptions. Thus, when we perceive a thing, we can have a conception of it - that is, we can grasp its form mentally. But the ideas that lie outside the province of the senses cannot be created by the soul, nor constructed by it essentially and independently. According to this theory, the mind merely manages the conceptions of sensible ideas. It does this either (1) by combination and division, so that it combines those conceptions, or divides every one of them. Thus, it conceives 'a mountain of gold', or divides 'the tree', that is had known into pieces and parts. Or (2) the mind manages the conceptions of sensible ideas by abstraction and universalization, so that it separates the qualities of the form, and abstracts the form from its particular qualities; with the result that [the mind] can form from it a universal idea. This is exemplified in conceiving Zayd, and discounting all that which distinguishes him from 'Umar. By means of this process of subtraction, the mind retains an abstract idea that applies to both Zayd and 'Umar.
Perhaps the first one to advocate this empirical theory was John Locke, the eminent British philosopher who emerged in a philosophical period pervaded by the Cartesian notions of innate ideas. Thus, Locke began to refute these notions. For this purpose, he put forth in his book, Essay on Human Understanding, a detailed philosophy of human knowledge. In this book, he attempted to attribute all conceptions and ideas to the senses. Lacer, this theory became widely spread among European philosophers, and, to some extent, it destroyed the theory of innate ideas. A number of philosophers adopted its most extreme (p. 65) forms. This led to very dangerous philosophies, such as the philosophies of Berkeley and David Hume, as we will show later, God willing.
Marxism adopted this theory in its explanation of human knowledge. This was consistent with its view of human consciousness as a reflection of objective reality. Thus, all knowledge can be attributed to a reflection of a particular reality. Such a reflection occurs by means of the senses. It is not possible for knowledge and thought to be related to anything that falls outside the limits of sensible reflections. Hence, we do not conceive anything other than our sense perceptions which indicate objective realities that exist in the external world.
Georges Politzer  said the following:
But what is the point of the origin of consciousness or thought? It is sense perception. Further, the source of the sense perceptions chat human beings experience is grounded in their natural needs. 
The Marxist view, therefore, can be interpreted to mean that there is no source for the content of our consciousness other than the objective particulars which are given to us by the external circumstances that we live. These particulars are given to us through sense perceptions. That is all there is to this matter. 
In an attempt to clarify the Marxist view of this matter, Mao Tse-tungn  made the following statement: 'The source of all knowledge lies hidden in the perceptions by the bodily human sense organs of the objective world which surrounds us.' 
Thus, the first step in the process of acquiring knowledge is (p. 66) the primary contact with the external environment - this is the stage of sense perception. The second step is the accumulation, the lining up and the organizing of the information which we gather from sense perception. 
The empirical theory focuses on experimentation; for scientific experiments have shown chat the senses [provide] the perceptions chat produce the human conceptions. Thus, he who is deprived of any sense cannot conceive the ideas that are related to that specific sense.
Such experiments - if sound- prove scientifically only that the senses are the primary source of conception. Were it not for the senses, no conceptions would have existed in the human mind. However, such experiments do not strip the mind of the ability to produce from the sensible ideas new ideas not known by the senses. Therefore, it is not necessary that all our simple conceptions be preceded by the sense perception of their ideas, as the empirical theory claims. In light of the above-mentioned experiments, the senses are the primary structure on the basis of which the human conception is established. But this idea does not mean that the mind is void of agency and innovation of new conceptions in light of the conceptions that are derived from the senses.
It is possible for us to show the failure of the empirical theory in its attempt to attribute all the human conceptual notions to the senses by investigating a number of the notions of the human mind, such as the following: 'cause' and 'effect', 'substance' and 'accident', 'possibility' and 'necessity', 'unity' and 'multiplicity', 'existence' and 'non-existence', as well as other similar notions and conceptions.
We all know that the senses grasp the cause and effect themselves. (p. 67) Thus, by means of our sight, we know that a pencil falls to the ground if the table on which it was placed is pulled from underneath it. Also, by means of touch, we know that water becomes hot when it is placed on fire. Similarly, we know chat bodily particles expand in hot weather. In these examples, we perceive two successive phenomena, but we do not perceive a specific relation between the two. This relation is what we call 'causality'. By 'causality' we mean the influence of one of these phenomena on the other and the need of the other for it, in order that the other exists.
The attempts that seek to extend the province of the senses to cover causality itself and to consider it as an empirical principle are based on avoiding the depth and precision in the knowledge of the realm of the senses and the ideas and limits it includes. Regardless of the proclamations made by the empiricists - namely, chat human experiences and the experimental sciences, which are based on the senses, are what clarify the principle of causality, and make us realize how specific material phenomena arise from other similar phenomena - I say that regardless of such proclamations, the empiricists will not be successful, as long as we know that scientific experiments cannot reveal by means of the senses anything except the succession of phenomena. Thus, we can know that by placing water on the fire, the water gets hot. Then we multiply its temperature. At last, we perceive the boiling of the water. The empirical side of the experiment does not disclose that boiling is produced because the temperature reaches a specific degree. But if our empirical experiments fall short of disclosing the notion of causality, then how did this nation develop in the human mind, so that we began to conceive it and think about it?
David Hume, one of the advocates of the empirical principle, was more precise than others in applying the empirical theory. He knew that causality, in the real sense of the term, cannot be known by the senses. Because of this, he rejected the principle of causality and attributed it to the habit of the association of ideas, saying that I see the billiard ball move, and then encounter another ball that, in turn, moves. But in the movement of the former ball, there is nothing that reveals to me the necessity of the movement of the latter. The internal senses also tell me that the movement of the organs follows upon an order from the will. However, they do not give me a direct knowledge of a necessary relation between the movement and the order.  (p. 68)
But the rejection of the principle of causality does not at all minimize the difficulty that faces the empirical theory. The rejection of this principle as an objective reality means that we do not believe that causality is a law of objective reality, and that we are unable to know whether the phenomena are linked by necessary relations that make some of them effects of some others. However, the principle of causality as an idea assented to is one thing, while the principle of causality as a conceptual idea is another. Suppose, for example, that we do not assent to the fact that some sensible things cause some other sensible things, and chat we do not form an assent concerning the principle of causality, would this mean that we do not have a conception of the principle of causality either? If we do not have such a conception, then what is it chat was rejected by David Hume? Can a human being reject something of which he has no conception?
The undeniable truth is chat we conceive the principle of causality, whether or not we assent to it. Further, the conception of causality is not composed of the conceptions of the two successive things. When we conceive the causation of a specific degree of temperature for boiling, we do not intend by this causation an artificial composition of the idea of temperature and that of boiling. Rather, we intend a third idea that exists between the two. From where, then, does this third idea that is not known by the senses come, if the mind does not have the ability to create non-sensible ideas? We face the same difficulty with regard to the other notions mentioned earlier;  since all of them are non-sensible. Thus, it is necessary to cast aside the purely empirical explanation of human conceptions and to adopt the dispossession theory (nazariyyat al-intiza).
IV - The Dispossession Theory
This is the theory of the Islamic philosophers in general. It can be summarized in the division of the mental conceptions into the following two kind:: primary conceptions and secondary conceptions.
The primary conceptions are the conceptual foundation of the human mind. (p. 69) These primary conceptions are produced from the direct genre perception of their content. Thus, we conceive heat because we had known it by means of touch. And, we conceive a color because we had known it by means of vision. Again, we conceive sweetness because we had known it by means of taste. Similarly, we conceive an odor because we had known it by means of smell. The same is true of all the ideas that we know by means of our senses. The sense perception of every one of them is the cause of their conception and the presence of an idea about them in the human mind. These ideas form the primary foundation of conception. On the basis of this foundation, the mind establishes the secondary conceptions. With this, the stage of innovation and construction begins - the theory under consideration gives this stage the technical name 'dispossession'. The mind produces new notions from those primary ideas. These new ideas fall outside the scope of the senses, even though they are derived and extracted from the ideas that are given to the mind and to thought by the senses.
This theory is consistent with demonstration and experiments. It is possible for it to give a solid explanation of all the conceptual units. In light of this theory, we can understand how the notions of cause and effect, substance and accident, existence and unity came about in the human mind. All of them are dispossessed notions that the mind invents in light of the sensible ideas. Thus, we perceive the boiling of water [at sea level] when its temperature reaches one hundred degrees [centigrade]. Further, our perception of rhea two phenomena -the phenomena of boiling and that of temperature - may be repeated a thousand times, yet without our ever perceiving the causation of temperature to boiling. Rather, the mind dispossesses the notion of causality from the two phenomena that are offered by the senses to the field of conception.
Due to the limitation of space, we cannot discuss the manner, kinds and divisions of mental dispossessions. This is because in this brief investigation of ours, we are not to discuss anything other than the main points. (p. 70)
Assent and Its Primary Source
We move now from the investigation of simple knowledge (conception) to the investigation of knowledge as assent that involves a judgement, and by means of which human beings obtain objective knowledge.
Every one of us knows a number of propositions and assents to them. Among such propositions, there are those in which the judgement is based on particular objective realities, as in our statements: 'The weather is hot.' 'The sun is out.' Because of this, the proposition is called 'particular'. There are also propositions in which the judgement is based on two general ideas, as in our statements: 'The whole is greater than the part.' 'One is half of two.' 'The indivisible part is impossible.' 'Heat causes boiling.' 'Coldness is a cause of solidification.' 'The circumference of the circle is greater than its diameter.' 'A mass is a relative reality.' The same is true of [other] philosophical, physical and mathematical propositions. These propositions are called 'universal' or 'general'. The problem that we encounter is that of knowing the origin of knowledge as assent and the principles on which the edifice of human knowledge is based. What, then, are the primary threads from which that large group of judgements and knowledge is woven? Also, what is the principle that human knowledge reaches in explanation, and is considered a general primary criterion for distinguishing truth from other things?
There are a number of philosophical doctrines concerned with this issue. Of these doctrines we will take up for study the rational doctrine and the experimental doctrine. The former is the doctrine on which Islamic philosophy, as well as the method of Islamic thinking in general, is based. The latter is the prevalent view in a number of materialistic schools, of which the Marxist school is one.
I - The Rational Doctrine
In the view of the rationalists, human knowledge is divided into two kinds. One of them is necessary knowledge, or intuitive knowledge. (p. 71) By 'necessity' here, we mean that the soul is obliged to accept a certain proposition, without having to require any evidence or a demonstration of its soundness. Rather, it finds in its own nature the necessity for believing it, in a manner not in need of any evidence or conformation. This is exemplified in the soul's belief in, or knowledge of, the following propositions: 'Negation and affirmation are not true of the same thing [at the same time].' 'That which is originated does not exist without a cause.' 'Contrary qualities are not in harmony in the same subject.' 'The whole is greater than the part.' 'One is half of two.'
The ocher kind consists of theoretical knowledge and information. There are a number of propositions whose truth the soul does not believe except in light of previous knowledge and information. Thus, the soul's making of judgements in those propositions depends on the process of thinking and derivation of the truth from prior truths that are clearer than they are, as in the following propositions: 'The earth is spherical.' 'Motion is a cause of heat.' '[The infinite] regress is impossible.' 'Bodily particles expand by heat.' 'The angles of a triangle are equal to two right angles.' 'Matter is transformable into energy.' The same is true of similar philosophical and scientific propositions. When such propositions are presented to the soul, the soul does not reach a judgement concerning them except after reviewing other information. Because of this, the theoretical knowledge depends on the necessary primary knowledge. Therefore, if such primary knowledge is removed from the human mind, one would not be able at all to attain any theoretical knowledge, as we will show later, God willing.
Thus, the rational doctrine shows chat the cornerstone of knowledge is the primary information. On the basis of such information, the superstructures of human thought, referred to as 'secondary information', are built.
The operation through which one derives theoretical knowledge from previous knowledge is the operation that we call 'thought' or 'thinking'. Thinking is an effort that the mind makes for the purpose of acquiring a new assent or a new knowledge from some of its previous knowledge. This means that when a human being attempts to deal with a new issue, such as the origination of matter, in order to know (p. 72) whether matter is originated or old, he has two things to consider. One of them is a specific attribute - that is, the origination. And the other is the thing which seeks actualization by means of acquiring that attribute - this thing being 'matter'. Since this proposition is not one of the rational primary propositions, a human being, therefore, would naturally hesitate to judge and to accept the origination of matter. He then resorts to his previous knowledge to try to find in it something on which he can base his judgement and utilize as an intermediary for knowing the origination of matter. With this, the process of thinking begins by looking over the previous information. Let us suppose, for example, that among such truths that the thinker already knows, there is the substantial movement that determines that matter is a continuous motion and a constant renewal. The mind, then, grasps this truth when this truth appears to it in the mental presentation, and makes it a link between matter and origination. For, since matter is renewable, is must be originated. This is because continuous change means continuous creation. At that point, a new knowledge is acquired by the human being, this knowledge being that matter is originated, because it is moveable and renewable, and whatever is renewable is originated.
This is how the mind is able to draw a link between origination and matter - the link being the motion of matter. It is this motion that makes us believe that matter is originated, because we know that everything moveable is originated.
Due to this, the rational doctrine asserts chat the causal relation in human knowledge is between some information and some other. For all knowledge is only produced by previous knowledge. The same is true of this previous knowledge, [and so on], until the progressive series reaches the primary rational knowledge that does not arise from previous knowledge. For this reason, this primary knowledge is considered the primary cause of knowledge.
This primary cause of knowledge is of two kinds: it is either (1) a basic condition of all human knowledge in general, or (2) a cause of a part of the information. The former is the principle of non-contradiction. This principle is necessary for all (p. 78) knowledge. Without is one cannot be sure that a certain proposition is not false, regardless of how much evidence one has for its truth and soundness. This is because, if contradiction were possible, then it would be possible for the proposition to be false at the same time in which we prove its truth. This means that the collapse of the principle of noncontradiction strikes a blow at all philosophical and physical propositions, regardless of their kind. The latter kind of primary knowledge is the rest of the necessary knowledge of which every piece is a cause of a group of pieces of information.
On the basis of the rational doctrine, the following [truths] hold: first, the primary criterion of human thinking in general is the necessary rational knowledge. It is the fundamental pillar that is indispensable in every field. The truth or falsity of every idea must be measured in light of it. Due to this, the field of human knowledge becomes wider than the sphere of the senses and experimentation. This is because it provides human thinking with powers that extend to truths and propositions that lie beyond matter, and achieves for metaphysics and the higher philosophy the possibility of knowledge.
The experimental doctrine is the contrary of this. It distances the metaphysical issues from the field of discussion, because they are issues which are not subject to experimentation, and to which scientific understanding does not extend. Thus, it is not possible to be sure whether they are negations or affirmations, as long as experimentation is the only primary criterion, as the experimental doctrine claims.
Second, in the view of the rationalists, the progression of thought moves from general propositions to more particular propositions - that is, from universal propositions to particular propositions. Even in the experimental field, which appears at first sight to be one in which the mind moves from individual experimental subjects to general principles and laws, movement and progression occur from the general to the particular. This will be shown in our response to the experimental doctrine. (p. 74)
No doubt, you remember the example already mentioned of the knowledgeability of thought, how we moved in it from a general knowledge to a particular knowledge. We acquired the knowledge that 'matter is originated' from the knowledge that 'everything that changes is originated'. Thought began with this universal proposition, 'Everything that changes is originated', and then moved from it to a more particular proposition, 'Matter is originated'.
Finally we must warn that the rational doctrine does not neglect the powerful role of experimentation in the human sciences and knowledge, the enormous services that experimentation offers to mankind, and the secrets of the universe and the natural mysteries that it discloses. However, according to this doctrine, experimentation alone could not have played this powerful role; because for the derivation of any such scientific truths from it, it requires the application of the necessary rational laws. This means that the derivation is achieved in light of the primary knowledge. It is not possible for experiments in themselves to be the original source and the primary criterion for knowledge. For it is analogous to the test that the doctor gives the patient. It is this test that provides the doctor with the opportunity of discovering the nature of the disease and its accompanying complications. However, this test would not help discover that, were it not for the previous information and knowledge that the doctor has. Had he not had such information, his test would have been null and empty of any benefit. Similarly, human experiments, in general, do not pave the way for conclusions and truths except in light of previous rational information.
11 - The Empirical Doctrine
This doctrine states that experience is the primary source of all human knowledge. For that, it relies on the assertion that when human beings are deprived of the various kinds of experiences, they do not know any truth, regardless of its clarity. This shows that  human beings are born without any innate knowledge. They begin their awareness and knowledge as soon as they begin (p. 75) their practical lives. Their knowledge widens as their experiences widen, and their knowledge becomes varied in kind as their. experiences take on different forms.
The empiricists do not admit necessary rational knowledge prior to experience. Rather, they consider experience as the only basis of sound judgement and the general criterion in every field. Even those judgements that the rational doctrine alleges to be necessary knowledge must, [according to the empiricists], be subject to the empirical criterion, and must be admitted in accordance with the determination of experience. This is because human beings do not have any judgement whose confirmation does not require experience. This results in the following:
First, the, power of human thinking is delimited by the limits of the empirical field; so that, any metaphysical investigation or study of metaphysical issues becomes useless. [In this, the empirical doctrine] is exactly the contrary of the rational doctrine.
Second, the movement of thought progresses in a way contrary to the manner asserted by the rational doctrine. Thus, whereas the rational doctrine asserts that a thought always moves from what is general to what is particular, the empiricists assert that it moves from what is particular to what is general; that is, from the narrow limits of experiments to universal laws and principles. It always progresses from the empirical particular truth to the absolute truth. The general laws and universal principles that human beings have are nothing but the result of experiences. The consequence of this is a progression of induction from  individual things to a discovery of general objective truths.
For this reason, the empirical doctrine relies on the inductive method in [its] search for evidence and in thinking, since this method is one that ascends from the particular to the universal. It rejects the principle of syllogistic  reasoning, by virtue of which thought moves from the general to the particular, as in the following syllogistic figure:  'All human beings are mortal.' 'Muhammad is a human being.' 'Therefore, Muhammad is mortal.' (p. 76) This rejection depends on the fact that this syllogistic figure does not lead to new knowledge in the conclusion, even though it is a condition of demonstration that it leads to a new conclusion not contained in the premises.  Thus, the syllogism in its above-mentioned form falls into the kind of fallacy called 'begging the question' (al-musadara 'ala al-matlub). This is because if we accept the premise 'all human beings are mortal', we then include in the subject, 'human being', all human individuals. After that, if we follow this premise by another: 'Muhammad is a human being,' we are then either aware that Muhammad is one of the human individuals we intended in the first premise - with this, we would also be aware that he is mortal before we state this truth in the second premise - or we are not aware of that. In this case, we would have generalized the first premise without justification, because we had not yet known that mortality is applicable to all human beings, as we claimed.
This is a brief exposition of the empirical doctrine which we find ourselves obliged to reject for the following reasons. First, is this principle itself (experience is the primary criterion for discerning the truth) primary knowledge that human beings acquire without previous experience? Or is it, in turn, like other human knowledge, in being neither innate nor necessary? If it is primary knowledge previous to experience, then the empirical doctrine, which does not affirm primary knowledge, is falsified; and the presence of necessary human information as independent of experience is affirmed. But if this knowledge is in need of previous knowledge, this would mean that we do not know at first that experience is a logical criterion whose truth is secured. How, then, can one demonstrate its truth, and consider it a criterion of experience when its truth is not yet certain?
In other words, if the above-mentioned principle, which is the cornerstone of the empirical doctrine, is false, then the empirical doctrine collapses due to the collapse of its main principle. (p. 77) If, on the other hand, it is sound, then it will be appropriate for us to inquire about the reason that led the empiricists to believe that this principle is sound. For if they were assured of its soundness without experience, this would mean that it is an intuitive proposition, and that human beings possess truths that lie beyond the realm of experience. If, however, they were assured of its soundness by a previous experience, this would be impossible, because experience cannot ascertain its own value.
Second, the philosophical notion that is based on the empirical doctrine is incapable of affirming matter. The reason for this is that matter cannot be disclosed by means of pure experience. Rather, all that appears to the senses in the experiential fields are only the phenomena and accidents of matter. Regarding matter itself - namely, the material substance that those phenomena and qualities exhibit - it is not known by the senses. The rose that we see on the tree, for example, or that we touch with our hand [is such that] we only have sense perception of its odor, color and softness. Even if we taste it, we will [only] have sense perception of its flavor. But in none of these cases do we have sense perception of the substance in which all these phenomena meet. Rather, we know this substance only by means of a rational proof that is based on primary rational knowledge, as we will point out in the forthcoming discussions. For this reason, a number of empiricists or experientialists denied the existence of matter.
The only ground for asserting [the existence of] matter are the primary rational propositions. Were it not for them, it would not be possible for the senses to confirm to us the existence of matter behind the beautiful smell, the red color and the specific flavor of the rose.
Thus, it becomes dear to us that the metaphysical realities are not the only realities whose demonstration requires the pursuit of the rational method in thinking, but also matter itself.
As a matter of fact, we raise this objection against those who believe on the basis of the principles of the empirical doctrine that a material substance exists in nature. But this objection does not touch those who interpret nature (p. 78) as mere phenomena that occur and change, without admitting a subject in which such phenomena meet.
Third, if the mind were confined to the limits of experience and did not have knowledge independent of experience, then it would not be possible for it at all to assert the impossibility of anything. This is because impossibility, in the sense of 'non-possibility of the existence of a thing', is not within the scope of experience; nor is it possible for experience to disclose it. The most that experience can show is the non-existence of specific things.  However, the non-existence of a thing does not mean its impossibility. There are a number of things whose existence is not disclosed by experience. Rather, experience shows their non-existence in their specific area. In spite of that, we do not consider them impossible; nor do we strip them of the possibility of existence, as we do in the case of impossible things. There is a clear difference between the collision of the moon with the earth, the existence of people on Mars, or the existence of a human being who can fly due to specific flexibility in his muscles, on the one hand,  and the existence of a triangle having four sides, the existence of a part greater than the whole, or the existence of the moon in the case of its non-existence, on the other hand.  None of these propositions has been actualized, and none of them has been subject to experience. Thus, if experience alone were the main source of knowledge, then we would not be able to distinguish between the [abovementioned] two groups [of propositions]. This is because the word 'experience' is the same in both of them. In spite of this, we all see the clear difference between the two groups. The first group has not been actualized; however, it is possible essentially. As for the second group, it is not only nonexistent, but it cannot exist at all. The triangle, for example, cannot have four sides, whether or not the moon collides with the earth. This judgement of impossibility cannot be interpreted except in light of the rational doctrine, as a rational knowledge independent of experience. Because of this, the empiricists are left with two alternatives only. They must either admit the impossibility of specific things, such as the things mentioned in the second group, (p. 79) or they must deny the notion of impossibility of all things.
If they accept the impossibility of things, such as those which we have mentioned [in the second group], their acceptance must rely on independent rational knowledge, and not on experience. The reason is that the nonappearance of a thing in experience does not indicate its impossibility.
If, on the other hand, they deny the notion of impossibility, and do not admit the impossibility of anything, regardless of how strange that may be to the mind, on the basis of such a denial, there would remain no difference between the two groups already presented, concerning which we have realized the necessity of differentiating between them. Further, if the notion of impossibility is eliminated, then contradiction - namely, the simultaneous existence and non-existence of a thing, or the simultaneous truth and falsity of a proposition - will not be impossible. But the possibility of contradiction leads to the collapse of all knowledge and' science, and to the failure of experience to remove doubt and hesitancy in any scientific field. This is because no matter how many experiments and pieces of evidence confirm the truth of a specific scientific proposition, such as 'Gold is a simple element', we still cannot be certain that this proposition is not false, as long as it is possible for things to be contradictory and for propositions to be true and false at the same time.
Fourth the principle of causality cannot be demonstrated by means of the empirical doctrine. As the empirical theory is incapable of giving a sound justification of causality as a conceptual idea, so also is the empirical doctrine incapable of demonstrating it as a principle or an idea of assent. For experience cannot clarify anything to us except a succession of specific phenomena. Thus, by means of it we know that water boils when it is heated to 100 degrees [centigrade], and that it freezes when its temperature reaches below 0 degrees [centigrade]. As for one phenomenon causing the other, and the necessity between the two, this is something not disclosed by the means of experience, regardless of how precise it is and regardless of our repetition of the experience. But if the principle of causality collapses, all the natural sciences also collapse, as you will learn later.
Some empiricists, such as David Hume and John Stuart Mill (p. 80), have admitted this truth. That is why Hume interprets the element of necessity in the law of cause and effect to be due to the nature of the rational operation that is employed in reaching this law. He says that if one of the operations of the mind is employed for the purpose of obtaining this law - adding that if one of the operations of the mind always leads to another operation that follows it immediately -then, with the passage of time, a constant strong relation, which we call 'the relation of association of ideas', develops between the two operations. This association is accompanied by a kind of rational necessity, such that the idea that is linked to one of the two mental operations occurs in the mind, as does the idea that is linked to the other operation. This rational necessity is the basis of what we call the necessity that we grasp in the link between the cause and the effect. There is no doubt that this explanation of the relation between the cause and the effect is incorrect for the following reasons.
First, from this explanation, it follows that we do not reach the general law of causality except after a series of repeated events and experiments that fasten in the mind the link between the two ideas of cause and effect, even though that is not necessary. For the natural scientist is able to infer a relation of causality and necessity between two things that occur in one event. His certitude is not at all strengthened [later] beyond what it was when he observed the event for the first time. Similarly, the relation of causality is not strengthened by the repetition of other events involving the same cause and effect.
Second, let us put aside two successive external events and turn our attention to their two ideas in the mind - namely, the idea of cause and that of effect. Is the relation between them one of necessity or one of conjunction, as our conception of iron is conjoined to our conception of the market in which the iron is sold? If it is a necessary relation, then the principle of causality is confirmed, and a non-empirical relation between two ideas - that is, the relation of necessity - is implicitly admitted. (p. 81) [In this case], whether necessity is between two ideas or between two objective realities, it cannot be demonstrated by sense experience. If, on the other hand, the relation is a mere conjunction, then David [Hume] did not succeed in explaining, as he intended, the element of necessity in the law of cause and effect.
Third, the necessity, which we grasp in the relation of causality between a cause and an effect, involves no influence at all on requiring the mind to invoke one of the two ideas when the other idea occurs in the mind. That is why this necessity that we grasp between the cause and the effect is the same, whether or not we have a specific idea about the relation. Thus, necessity of the principle of causality is not a psychological necessity, but an objective necessity.
Fourth, the cause and effect may be completely conjoined, yet in spite of that, we grasp the causation of the one on the other. This is exemplified m the movement of the hand and that of the pencil during writing. These two movements are always present at the same time. If the source of necessity and causality were the succession of one of the two mental operations after the other by means of association, then it would not be possible in this example for the movement of the hand to play the role of the cause loll the movement of the pencil; for the mind grasps the two movements at the same time. Why then should one of them be posited as a cause and the other as an effect?
In other words, explaining causality as a psychological necessity means that the cause is considered as such, not because in objective reality it is prior to the effect and is productive of it, but because knowledge of it is always followed by knowledge of the effect by means of the association of ideas. Due to this, the former is the cause of the latter. This explanation cannot show us how the movement of the hand becomes a cause of the movement of the pencil, even though the movement of the pencil does not succeed the movement of the hand in knowledge. Rather, the two movements are known simultaneously. Thus, if the movement of the hand does not have actual priority and objective causality over the movement of the pencil, it would not have been possible to consider it as a cause. (p. 82)
Fifth, it is often the case that two things are associated without the belief that one of them is a cause of the other. If it were possible for David Hume to explain the cause and effect as two events whose succession we often grasp, such that a link of the type of association of ideas occurs between them in the mind, then the night and day would be of this sort. As heat and boiling are two events that have succeeded each other, until an associational link developed between them, the same must be true of the night and day, their succession and their association, even though the elements of causality and necessity that we grasp between heat and boiling are non-existent between the night and day. The night is not a cause of the day, nor the day a cause of the night. It is not possible, therefore, to explain these two elements by the mere repeated succession which leads to the association of ideas, as Hume tried to do.
We conclude from this that the empirical doctrine unavoidably leads to the elimination of the principle of causality and to the failure of demonstrating necessary relations between things. But if the principle of causality is eliminated, all the natural sciences will collapse, since they depend on it, as you will know.
The natural sciences, which the empiricists seek to establish on the basis of pure experimentation, are themselves in need of primary rational principles that are prior to experimentation. This is because the scientist carries out his experiment in his laboratory on limited objective particulars. Then he puts forward a theory for explaining the phenomena that the experiment in the laboratory had disclosed, and for justifying them by one common cause. This is exemplified in the theory that states that the cause of heat is motion, on the basis of a number of experiments interpreted in this way. It is our right to ask the natural scientist about how he offers this theory as a universal law applicable to all circumstances resembling those of the experiment, even though the experiment did not apply except to a number of specific things. Is it not the case, then, that this generalization is based on a principle stating that similar circumstances and things alike in kind and reality must share in laws (p. 83) and decrees? Here, once again, we inquire about how the mind reached this principle. The empiricists cannot claim that it is an empirical principle. Rather, it must be a piece of rational knowledge that is prior to experimentation. The reason is that if it were supported by experimentation, then the experimentation on which this principle is based also, in turn, treats only specific subjects. How, then, can a general principle be based on it? Thus, the establishment of a general principle or a universal law in light of one or more experiments cannot be accomplished except after admitting prior rational knowledge.
With this, it becomes clear that all the empirical theories in the natural sciences are based on a number of pieces of rational knowledge that are not subject to experimentation. Rather, the mind accepts them immediately. They are the following:
- 1. The principle of causality, in the sense of the impossibility of chance. That is, if chance were possible, then it would not be possible for the natural scientist to reach a common explanation of the numerous phenomena that appear in his experimentation.
- 2. The principle of harmony between cause and effect. This principle states that things that in reality are similar necessarily depend on a common cause.
- 3. The principle of non-contradiction that asserts that it is impossible for negation and affirmation to be true simultaneously.
If the scientist accepts these pieces of knowledge that are prior to experimentation, and then carries out his various experiments on the kinds and divisions of heat, he can, in the last analysis, postulate a theory for explaining the different kinds of heat by one cause, such as motion, for example. On the whole, it is not possible to postulate this theory as a decisive and an absolute one. The reason is that it can be such only if it is possible for one to be certain of the absence of another explanation of those phenomena, and of the incorrectness of explaining them by another cause. However, in general, this is not determined by experiments. (p. 84) That is why the conclusions of the natural sciences are, for the most part, presumptive, due to a deficiency in experiments, and to an incompleteness in the conditions that make them decisive experiments.
It becomes clear to us from what has preceded that the inference of a scientific conclusion from an experiment is always dependent on syllogistic reasoning in which the human mind moves from the general to the specific, and from the universal to the particular, exactly as viewed by the rational doctrine. The scientist is able to draw the conclusion in the above example by moving from the already mentioned three primary principles (the principle of causality, the principle of harmony, and the principle of non-contradiction) to that specific conclusion in accordance with the syllogistic approach.
Regarding the objection raised by the empiricists against the method of syllogistic reasoning- namely, that the conclusion in it is nothing but an echo of one of the two premises, that is, the major premise, and a repetition of it- it is a bad objection, according to the teachings of the rational doctrine. This is because if we intended to demonstrate the major premise by experiments, and had no other criterion, then we would have to examine all the divisions and kinds, in order to be certain of the soundness of the judgement. The conclusion then would have been also determined in the major premise itself. But if the major premise were a piece of rational knowledge, which we grasp without need of experiments, such as the primary intuitive propositions and the rational theories that are derived from such propositions, then he who seeks to demonstrate the major premise does not need to examine the particulars so that the conclusion is necessitated to take on the quality of repetition and reiteration.  (p. 85)
Once again, we assert that we do not deny the great value of experience for humanity and the extent of its service in the fields of knowledge. However, we wish to make the empiricists understand that experiments are not the primary criterion and the fundamental source of human thought and knowledge. Rather, the primary criterion and the fundamental source are rational primary information, in whose light we acquire all other information and truths. Even experience itself is in need of such a rational criterion. Thus, we and others alike are required to admit this criterion on which the principles of our metaphysical philosophy are based. If, after that, the empiricists attempt to deny this criterion in order to falsify our philosophy, they would be, at the same time, attacking the principles that are the foundation of the natural sciences, and without which the empirical experience is completely fruitless.
In light of the rational doctrine, we can explain the quality of necessity and absolute certainty that distinguish mathematics from the propositions of the natural sciences. This distinction is due to the fact that the necessary mathematical laws and truths are supported by the primary principles (p. 86) of the mind, and do not depend on the discoveries of experiments. The scientific propositions are contrariwise. Thus, the expansion of iron due to heat is not one of the propositions that are given by those principles with no mediation, but is based on experimental propositions. The decisive rational character is the secret of the necessity and absolute certainty in the mathematical truths.
If we study the difference between the mathematical and the natural propositions in light of the empirical doctrine, we will not find a decisive justification for this difference, as long as experience is the only source of scientific knowledge in the two fields.
Some of the defenders of the empirical doctrine have tried to explain the difference on a doctrinal basis by saying that the mathematical propositions are analytic, and that it is not their function to come up with something new. When we say, for example, 'Two plus two equals four,' we do not say anything against which we can test the degree of our certainty, since 'four' is itself another expression for 'two' plus 'two'. Put clearly, the above-mentioned mathematical equation is nothing other than 'Four equals four'. All mathematical propositions are an extension of this analysis. However, this extension varies in the degree of its complexity.
The natural sciences, on the other hand, are not of this sort. The reason for this is that their propositions are composite; that is, the predicate in them adds new information to the subject. This is to say that it provides new
information on the basis of experiments. Thus, if you say, 'Water boils under such and such a pressure; that is, when its temperature, for example, reaches 100 degrees [centigrade]', then I would be informed that the term 'water' does not include the terms 'temperature" pressure', and 'boiling'. Because of this, the scientific propositions are subject to falsity and truth.
But, it is our right to remark concerning this attempt at justifying the difference between the mathematical and the natural propositions that the consideration of the former as analytic does not explain the difference on the basis of the empirical doctrine. Suppose that 'Two plus two equals four' is another expression for our statement, 'Four is four'. This would mean that this mathematical proposition depends on accepting the principle of non-contradiction; otherwise, 'four' may not be itself, if contradiction were (p. 87) possible. According to the teachings of the empirical doctrine, this principle is not rational and necessary; for it denies all prior knowledge. Rather, it is derived from experience, as are the principles on which the scientific propositions in the natural sciences are based. Thus, the problem remains unsolved, as long as both mathematics and the natural sciences are dependent on empirical principles. Why, then, are the mathematical propositions distinguished from other propositions by absolute necessary certainty?
Further, we do not admit that all mathematical propositions are analytic and an extension of the principle 'Four is four'. How could the truth stating 'The diameter is always shorter than the circumference' be an analytic proposition? Are 'shortness' and 'circumference' included in the notion of 'diameter'? And is 'diameter' another expression for the statement, 'The diameter is a diameter'?
We conclude from this study that the rational doctrine is the only doctrine capable of solving the problem of the justification of knowledge, and setting up the criteria and primary principles of knowledge.
Still, it remains for us to study one point concerning t