Basically, the rulings that had been made by the Companions and Successors were often based on their own understanding for the spirit and Shariah purpose. So, the rulings that are made by the Companions and Successors are not in restricted manner and also not in giving the exact meaning of the rules because they are not literalist. Therefore, istihsan has been made as the antidote to literalism which gives a wide interpretation of the law in order to sustain equality and also righteousness which is considered as the fifth role of istihsan
. For instance, oral evidence is the regular type of gaining the evidence and proof in Islamic law
. Normally, in oral evidence it needs two upright (â€˜adl) witnesses except if the law had stated otherwise for instance in proving zina (adultery), it needs to have four witnesses in order to prove adultery. Al-Quran had clearly stated regarding the matter of number of witnesses that are needed however as for the matter on how to gain the evidence it had been determined by using consensus that it should be made verbally. The Muslim jurists believe that the direct testimony of a witness in front of the judge without any intermediary is the best way of discovering the truth. However, the question that arises is that whether one should still insist on oral testimony at a time when there are other methods like photography, sound recording, laboratory analyses, etc. which provide equally in order to establish the truth. Thus, alternative ruling should be taken into account while departing from the established rule. By using istihsan it would validate these new techniques in order to uphold the spirit of establishing the truth rather than just using oral testimony to establish the truth
. By looking at the oral testimony example, it can be seen clearly that the Companions and Successors had given specific type of method in order to establish the truth which is oral testimony but by using istihsan the methods of proving the truth should be broaden by not only giving oral testimony but also other methods like photography and sound recording. Therefore, it show us that istihsan does have the role of as an antidote to literalism in which it had taken the broader way in order to bring justice and fairness. Another role of istihsan is that it is a principle which approves the parting from an established rule with another ruling which is stronger compared to the previous ruling.
It can be seen clearly by looking at the definition that had been given by IbnTaymiyyah
which is one of the Hanbaliâ€™s jurist
. IbnTaymiyyah said that istihsan is the desertion of one authorized rule (hukm) with another rule which is more better or stronger on the basis of the Al-Quran ,Sunnah or consensus.
In addition, Abu Zahrah
which is one of the Hanafiâ€™sjurist had stated that the essence of istihsan is to formulate a decision which sets apart an established analogy where by doing such withdrawal to the ruling can maintain the greater meaning of the Shariah
. In addition, according to the majority of jurists, istihsan involves the departure from qiyas jali (obvious analogy) to qiyas khafi (hidden analogy).
Qiyas Jali is a straightforward qiyas or clear qiyas where can be easily intelligible to the mind. Example of qiyas jali can be seen in the analogy between wine and herbal drink where herbal drink is considered as drink that can cause intoxication. Both wine and the herbal drink had the same effective cause (illah) which of being intoxicating. However, qiyas khafi can be defined as a form of analogy where it is not clear or obvious which cannot be seen to the naked eye and it will only be intelligible through a deeper thought. Qiyas khafi which can also be called as istihsan is better and also more operative in keeping away the hardship compared to qiyas jali. This is because qiyas khafi does not arrived from shallow thought of similarities but it had been done by going through deeper thoughts and analysis.
When the jurist faced upon a problem which there is no ruling can be found in the Al-Quran or Sunnah then the jurist can pursuit in looking for a ruling and also try to find the best resolution by using analogy. The act of jurist to find for the best alternatives will end up with two different resolutions; where one that are based on an obvious analogy and another one which is based on the hidden analogy. However, if there are any clashes between the two analogies then the prior analogy must be overruled by the latter analogy. The hidden analogy is more preferable compared to the obvious analogy and this is one form of istihsan. An example of istihsan that consist of parting from qiyas jali to qiyas khafi is in waqf (charitable endownment) of cultivated land which comprises the assignment or transferring of all the additional rights which are attached to the property like the right of water, right of passage and right of flow. Even though, all the ancillary rights are not explicitly stated in the waqf itself but it will be considered that the waqf is valid and this ruling is based on qiyas khafi (istihsan)
. To explain it in further, it can be seen that in Islamic law of contract, the contract of sale must clearly mentioned the object of contract and if it is not specified then it will not be included. By looking at this ruling, we can make a direct analogy (qiyas jali) between sale and waqf because both involve in transfer of ownership. Thus, it can be concluded that if the additional rights had been explicitly stated in the waqf then only it will be included in the waqf but if it does not explicitly stated in the waqf then it will not be included in the waqf. The issue that arise is that this direct analogy (qiyas jali) if being followed, it will lead us to unequitable results where the waqf of cultured lands that are without its additional or ancillary rights would prevent the essential rationale of waqf which is to ease the use of property for charitable purposes. Therefore, in order to avoid this hardship, an alternative analogy should be taken into account where it is called qiyas khafi (istihsan). In this case, the qiyas khafi is to draw similarity with the contract of lease (ijarah) and not with contact of sale. Both ijarah and waqf can be compared to each other because both also involve the transfer of usufruct. By using the alternative analogy, it can be said that waqf is included even without explicitly specify the ancillary rights of the property
. Other than that, there is another type of istihsan which is called as exceptional istihsan (istihsanistithnaâ€™i) where the role of this type of istihsan is to make an exception to the general rule of the present law when the jurist believed that by making such exception, justice and equity will be uphold better.
The decision that the jurist had made is as a result of the jurist personal ijtihad or the exception had been supported by the nass (Al-Quran and Sunnah), ijmaâ€™, approved custom, necessity (darurah), or considerations of public interest (maslahah)
. One of the example of exceptional istihsan that had been supported by the Al-Quran is regarding bequests to relatives ( Surah Al-Baqarah 2: 180). This Quranic verse signifies the exception from the general rule of Shariah where that a bequest (inheritance) is basically not valid because bequest controls the partition of the land once the testator had died and the new rule do not allow the act of quicken the process of bequest. Since a bequest although had been made while the testator was alive but it will only be effective after the testator had died, it is basically ultra vires and it is an equivalent to an intervention in the rights of the legal heirs
. However, the Al-Quran had permitted bequest to be an exception to the general principle where it considers a fair distribution of wealth in the family by way of exceptional istihsan
. Another example of exceptional istihsan can be seen based on necessity (darurah) where regarding on the method of adopting for the purification of polluted wells. Water in a well cannot be used for ablution if it has been polluted by impure substances and the water in the well also cannot be purified by removing the part which is impure. It also cannot be poured either because of the continuous contact with the water that flows in the well. In order to solve this matter, it had been found through istihsan where wells that had been contaminated can be cleansed by eliminating particular amount containers of water from the well. The precise amount of containers of water that should be eliminated from the contaminated well will be determined by looking at the type and the intensity of pollution that had been made. In this matter, istihsan had prevented human from going through hardship by reason of necessity
. Moreover, istihsan can also be used as a method that can improve the existing law where it can strip of the unreasonable and unwanted components in order to enhance it by making necessary exceptions.
In other words, basically istihsan functions within the boundaries of the current situation and it does not pursue a fundamental amendment in the present law even though it has the potential to effect innovation and refinement. Usually judges and lawyers are unwilling to advance from the present law or to make any exceptions even if there are evidence that clearly shows that the departure will bring fairness and justice. This is due to the judgeâ€™s role itself where they need to enforce and follow the law in whatever means. Therefore, it is advisable if the legislature can allow the judges to use istihsan in cases where that is the only way in order to achieve justice and fairness and it also can improve the existing law to be much better
Shah Abdul Hannan. Istihsan (Juristic Preference).Retrievved from http://thequranblog.files.wordpress.com/2010/04/istihsan.pdf 
Mohammad HashimKamali. (1991). Principes of Islamic Jurisprudence (2nd ed.). Ilmiah Publishers. 
Mohammad HashimKamali. Istihsan and The Renewal of Islamic Law. Retrieved from http://www.google.com.my/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0CCwQFjAC&url=http://www.iais.org.my/e/index.php/publications-sp-1447159098/articles/item/download/33_eb478d70dc61015675330077d946987b.html&ei=PiLyU9HVIcGcugSKqoCoDA&usg=AFQjCNG8Q1FNiaBt5l6swEFewJq_qDMWRw&sig2=DyXYDy-5VYu9ppxaLm6tPg 
Mohammad HashimKamali. (1991). Principes of Islamic Jurisprudence (2nd ed.). Ilmiah Publishers.