Chapter 1: Comparative Study of Tusi and Aristotle’s Shared Views on Philosophy


Khajeh Naseeroddeen Tusi was one of the great scholars of mathematics, astrology and wisdom in Iran in the seventh century of the Hejira. He was also one of the ministers of that time and a great jurisprudent of Shiite Islam. Khajeh wrote numerous books regarding different sciences (Moin, 1992). Khajeh Naseer Tusi had also compiled very valuable works in ethics and education (Beheshti, Abujafari and Faqihi 2000, P. 113).

Khajeh Tusi was born in Tus or in Jahrud of Qom, in 597 A.H. He died in Baghdad, in 672 A.H. (Modarresi, 2000). Khajeh spent his childhood with those who, according to him, were pious, religious, and aware of some sciences, occupations and crafts. His father was an experienced person, and always encouraged him to learn different techniques and sciences. He encouraged him to listen to the speech of those who practiced their religion with consciousness.

Naseeroddin emigrated from Tus to Neishapur and travelled to some other cities to complete his education. Two of his important activities were the establishing of the very great observatory of Maragheh, and a great library in Maragheh, which had 400 thousand books. He planned to allow thinkers to continuously extend their research and keep the great heritage of Islam alive.

Tusi himself wrote about 274 books. Most of his writings concerned philosophy, theosophy, mathematics, astrology, and ethics. His writings could be classified under the following ten titles: mathematics, ethics, interpretation, religious jurisprudence, history, geography, medicine, logics, theosophy, and philosophy (Beheshti, Abujafari and Faqihi, 2000, p. 113 -121).

In spite of the fact that Khajeh Naseer Tusi was making an effort to promote his own religion and belief (Shiite, Islam), he was very kind to other religious groups of Islam. He respected the scholars of each class or religion and refrained from rigid religious intolerance and dogmatism. This was the reason why some Christian orientalists, some Sunni scholars and all of Shiite scientists have highly esteemed his spiritual greatness, religiosity, humility and good manners (Modarresi, 2000).



Tusi believed that the First Origin was not possible in existence. This origin could not be more than one. He also asserted that a wise person would not engage much in the bodily pleasures (Modarresi, 2000, p. 171-172).


Tusi’s works and writings revealed the following views about the characteristics of a human being (Behesht, Abujafari and Faqihi 2000, p. 122-129):

The superiority of human being

According to Tusi human being was superior in creation to inanimate objects, plants and animals because they possessed a soul with intellect, reason and free will besides their other characteristics.

The truth of human being

Tusi believed that a human being consisted of body and a soul. This soul was free of material form. The body and soul both interacted with each other.

The faculties of the soul

In spite of its unity, the soul with intellect consisted of diverse animal, animal-like and human faculties. It possessed mobility and perceptive faculties. Man’s perceptive functions were carried out through external senses such as sight, hearing, smelling, taste, and touch as well as through inner senses such as common sense, imagination, estimate and memory. While the mobility of a man remained a function of his muscles, it was the soul that made him move toward the behavior for which he was motivated.

Free will and authority

These two were considered to be innate characteristics of a human being. Only the humankind could achieve perfection and happiness through their intention, deeds and behaviors. In this way, man could move towards perfection and attain status higher than that of angels.

It was in the light of free will that a man comprehended something and then found himself inclined or averse to it. Thus knowledge and enthusiasm formed the basis and foundation of human free will.

The problem of determinism could also be solved with this principle as humans behaved according to their authority and freewill. If they did not want, they would not engage with those behaviors. On the other hand, it was God who had wanted to give such authority and freewill to humans due to which they could freely engage with or not with a behavior.


The most outstanding privilege that mankind had, was their rationality. Humans not only possessed sensory and intellectual perception to recognize and solve their conceptual and affirmation of unknown things and extend their awareness, they also had knowledge of the present and non-present.

Tusi introduced rationality, knowledge and awareness as the greatest bounty that God had bestowed upon His bondmen, after their existence itself.

Being sociable

Tusi believed that no one could satisfy his or her needs alone without assistance and cooperation from others. On the other hand, cooperation of individuals was needed in order to achieve perfection and better enjoyment of different bounties from God

Complimentary and evolutionary movement

Man’s soul had different potential powers, and in trying to achieve perfection, he should nurture his abilities to reach closer in nearness to God. Man could make his freewill a function of the Divine freewill, and achieve the position of being contented first and subsequently attain positions of trust, submission and finally that of infinite knowledge and power and being eternal where there would be no veil between God and him.

Achieving the Position of nearness to God

One of the characteristics of human beings was the fact that they could reach a position of nearness to God. This position had different ranks and human beings were able to attain this position in various degrees. Therefore, although man had been expelled from Paradise, he could again, through servitude and submission to God, ascend and return to his first and original abode. To achieve this, he had to purify himself in the field of knowledge and action.

Tusi maintained that human soul was simply an essence, which could be perceived through intellect and could affect the sensory body. That essence itself was not the body. It was neither physical, nor sensory for any of the senses. Intellect of the soul remained unaffected even after destruction of one’s body. Death could not destroy the soul, and it could never be destroyed. Man’s body was like an instrument for the soul (Adamson 1998, p. 94-102).


Aristotle was convinced that the characteristic, which determined a thing’s nature, was what determined its successful operation, that is, its ability to achieve what was good for itself (as is implicit in his ethical writings).

A species became the one it was in its present form through its goals and by being organized in a way so as to achieve them. Some goals were extrinsic; for example, the goal of an axe being to cut wood explained the arrangement of the metal on the axe. Likewise, the teleological goal of man was to live a life of a given kind (e.g. of rational activity), and the rest of his nature was designed to achieve this intrinsic goal. The distinctive goal of each biological kind was what determined its respective essence (Honderich, 2005, p. 56).

Aristotle believed in the fact that it was the Pure One who was the cause of all things and was unlike any of them (Adamson, 2008). According to Aristotle, things could be a cause of one another, causing each other reciprocally, as hard workout produced fitness and vice versa. Aristotle further marked out two modes of causation: proper (prior) causation and accidental (chance) causation. All causes, proper and incidental, could be spoken of as potential or as actual, particular or generic (Wikipedia, 2008).



Tusi considered sensory perception as the first step towards cognition. Knowledge from imagination arose from the perception of material objects with all its characteristics whether that object was present or absent. Estimated knowledge was said to be from perception of non-sensory partial meanings of a situation, such as man’s fear of darkness. Intellectual knowledge was considered to be the real cognition as it was a perception of intellect. An object was thus perceived as a whole by including aspects that were the properties of matter and abstract from it.

Knowledge of intuition was deemed higher than knowledge of intellect. This kind of knowledge brought humans to a position from where they could observe the realities of the Universe. Undoubtedly the knowledge of a person, who saw fire from nearby and observed its light, was greater than that of one who knew about fire from a distance only through seeing its smoke.

Divine knowledge was the effusion of knowledge from exalted God Himself. It was received without direct instruction or thinking. Tusi was not convinced that the human intellect alone could answer the ultimate metaphysical questions (ibid). From his early life al-Tusi had believed that the rationale of intellect needed to be sustained by a non-rational (or super-rational) guarantor. His move to Twelver Shiism, with its doctrine of a hidden Imam, indicated growing strength of his convictions about the ability of the intellect (Cooper, 1998).


Aristotle believed that human understanding was analogous to a sensation. Intellect was a sense in itself (Genest, 1998). Aristotle’s remarks on how we came to know about the starting point of a matter, was somewhat baffling. What was clear however was that while he considered sensory perception to be a crucial ingredient in the process of coming to know, sensory perception by itself did not constitute knowledge. This was because sensory perception was able to show us only particular aspect of an object.

Real knowledge by definition pertained to the universal characteristics of things. One thus needed to be able to grasp the universal characteristics that presented itself in a material form, which imparted the sensory information. Aristotle showed no lack of confidence in the ability of human beings to do this reliably. However, this was no surprise.

It was clear that he conceived the world to be ordered in a way that made it comprehensible. And, human beings had the capacities necessary to achieve this understanding more notably through their rationality. However, he stressed, particularly in his ethical work, that one could not expect to achieve complete precision in all subjects (Irwin and Fine, 2008).

Aristotle’s philosophy was aimed at the Universal. Aristotle found the Universal in the particular aspect of things. He called it to be the essence of a thing. For Aristotle, philosophical method implied advancing from the study of particular phenomena to knowledge of essences. Aristotle’s method was both inductive and deductive (Wikipedia, 2008).




Tusi explained the foundation of his ethics on the bases of anthropology and epistemology. Some of the most important points that he proposed in this field were as follows (Beheshti, Abujafari and Faqihi, 2000, p.134-141):

A disposition was a firm faculty of a person’s soul. It was due to this disposition that their behavior was carried out easily. This disposition of man lay behind their nature and habits. Tusi believed that humans could save their souls from becoming base and from darkness. By doing so, they could achieve the highest ranks of perfection and reach closer to God.

Tusi considered ethics in two sections: keeping up of virtues and values, and treatment of diseases of the soul. Tusi believed that a man’s morality was changeable, although changing of some dispositions might be difficult. He asserted that people by nature were susceptible to virtues, happiness and wickedness. The human nature tended towards virtues or vices that had been placed in man’s nature.

Besides this, the natures of people were different. Some natures that tended towards happiness and virtues had greater readiness to accept virtues and goodness. However, some turned to vices as they had greater readiness for these. Importantly, each person was capable of changing his or her morals, habits and faculties.

According to Tusi moral education should be carried out depending on the stage of natural development of mankind. Moreover, while every person should be engaged in their own soul’s refinement, their faculties had to be guided through correct moral plans that were consistent with the development of their natural abilities.

Cognition of pleasure and pain played a major role in causing man to turn toward virtues and to keep away from vices, in Tusi’s view. He maintained that pleasures and pains were of two kinds: sensory and intellectual. Man comprehended sensory pleasures through his external and superficial senses, such as the pleasure of eating, drinking and sleeping. However, intellectual pleasures are not comprehended by the external senses.

Sensory pleasures were often experienced together with pain; these along with other pleasures were fleeting in nature. For this reason, even if someone were aware of their deficiencies, they would undoubtedly overlook them to pursue easily accessible intellectual and sensory pleasures. However, even though the ultimate aim of human being was to achieve happiness through purification and perfection of the soul, this happiness could not be obtained through any of the sensory pleasures.

Real happiness was understood to be pure pleasure free from pains and difficulties. It was based on wisdom, courage, chastity and justice. The one who attained real happiness would never grieve and nor could be annoyed due to decay of superficial pleasures and bounties. The real happiness was a constant, durable and unchangeable fact and was not affected by life’s difficulties and adversities.

Tusi maintained that different kinds of virtues were all based on wisdom, courage, chastity, and justice. Therefore, no one became worthy of praise unless he or she had gained one or all of these virtues (Zadeh, 1998, p.127).

Tusi was of the opinion that a human being was higher in spiritual ranking and virtue to other creatures. A person could reach the highest spiritual position, or could descend to lowest ranks in life. Man’s perfection and virtue were ensured through thinking, reason and wanting. His own hands held the keys to happiness, wickedness, development or deficiency.

If a person tended to be on the straight path, sciences, knowledge, manners and virtues, he would finally attain nearness to God. However if he moved toward corruption and worldly lusts, he would merely become deficient day by day and finally be destroyed. Therefore it was really necessary for all human beings to have a divine guide to show and lead them to their real goal for which they had been created (Zadeh, 1998, p.103-112).

A happy and virtuous person was one who used his aptitudes and powers to attain the virtue for which he had been created (ibid, p. 116).


In ethical theory, Aristotle used human nature to determine good life. While everyone considered a good life to be about happiness, people did not agree upon what that happiness consisted of. According to Aristotle, the answer depended on the understanding about who the human beings were essentially with regards to their distinctive function.

A distinctive human life was lived in accordance with reason. Consequently a good life for human beings was a life of reason lived ‘with excellence’ (or ‘with virtue’). Happiness or the good life involved functioning well in life.

Aristotle seemed to waver between declaring the good life to be a life dominated by a single activity namely contemplation of the results of (theoretical) reasoning or a life inclusive of many different activities (Mautner, 2005, p. 46). He suggested that well-being consisted of activity towards excellence such as intellectual contemplation and virtuous actions that stemmed from a virtuous character.

Virtuous action was what a person with practical wisdom would choose; and the practically wise were those who deliberated successfully towards well-being. This might be termed the Aristotelian circle because the key terms, (well-being, virtue,and practical wisdom) appear to be interrelated. Aristotle developed a theory of virtue, which aimed to explain the fact that what was good seemed to be so to the virtuous.

Man, if he was to achieve well-being as a human being, needed friendship and other directed virtues (such as courage, generosity, and justice). On occasions, Aristotle seemed to find his account of the good life to be based on a background assumption about the human nature. At other places, he based his account of human nature on what was good for the human beings to achieve. He remarked that the virtuous saw that which was good. In another place he wrote that what was good was so because it appeared to be good to the virtuous (Honderich, 2005, p 55).

Aristotle distinguished between moral excellence and intellectual excellence - one was attained through habits and the other through learning. Moral excellence was the acquired rational capacity to choose the way between extremes, for example, courage is the tendency to act with right amount of boldness to avoid cowardly fear on one hand and foolish overconfidence on the other (Mautner 2005, p. 46).

Aristotle taught that virtue had to do with the proper function of a thing. An eye was a good eye only in so much as to how well it could see because the proper function of eye was sight. Aristotle reasoned that a person must have a function that was not common to anything or anyone else, and that this function must be an activity of their soul. Aristotle identified the best activity of the soul as eudemonia - a happiness or joy that pervaded good life.

Aristotle thought that to achieve good life, one must live a balanced life and avoid any excess. This balance varied for different persons and situations. It existed as a golden mean between two vices - one was excess and the other was deficiency (Wikipedia, 2008).


Tusi believed that a ‘First origin’ was not possible for existence as origin could not be more than one. Aristotle believed that the ‘Pure one’ was the cause for all things and was not like any of the other existing things.

Tusi also believed in superiority of human beings in comparison to other creatures. Human beings possessed soul with intellect, reason and free will. Man consisted of both - a body and the soul, the soul being free from material form. Human soul was simply an essence. The soul with its intellect remained as such after the destruction of body.

According to Aristotle the teleological goal of man was to live life of a given kind (e.g. of rational activity). The ability to think for this purpose had been given to mankind. Human beings were superior to other creatures in this ability. They also had a spirit, in addition to the body. It was this spirit that gave them their main characteristic.

Tusi asserted that a man’s perception was carried out through his external and internal senses. Knowledge or episteme could be sensory, imaginary, estimated, intellectual, intuitional, divine and revealed. In this regard Aristotle asserted that sense perception was the crucial ingredient in the process of coming to know, but that sensory perception by itself did not constitute knowledge.

Tusi maintained that a moral disposition existed, which imparted nature and habits to a man. Human beings could save their souls from inferiority and darkness, achieving highest of ranks in perfection by reaching closer to God through directing their soul towards the good and virtues.

Pleasures and pains were of two kinds: sensory and intellectual. Intellectual pleasures could not be comprehended by the external senses. The ultimate aim of a human being was to gain happiness through purification and perfection of the soul. This happiness was achieved through sensory pleasures.

Real happiness was a pure pleasure free from pains and difficulties and was based on wisdom, courage, chastity and justice. All the other kinds of virtues were based on these fundamental attributes or characteristics.

It was necessary for all human beings to have a divine guide to show and lead them to the real goal for which they had been created. According to Aristotle, happiness and the good life consisted of functioning well in life. A distinguished human life was lived in accordance with reason. A person with practical wisdom would choose virtuous actions for his life.

Moral excellence and intellectual excellence were acquired through habit formation and learning respectively. Moral excellence was an acquired rational capacity to choose a balance between two extremes. To achieve the good life, one must live a balanced life and avoid excess.


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