Islamic scholars have their own scientific methods that they follow in order to extract a verdict. This science is called usool al fiqh, and is a very large subject that can be studied in hundreds of Islamic books.There is a difference between crime and sin when Fiqh developed as an independent science five categories were made fard which means obligatory act, haram is the forbidden acts, makruh is acts that are not recommended, mandub are praiseworthy acts and mubah is an cat which is not prohibited nor commanded by the Shariah law. Haram and makruh acts can be punishable in some Muslim countries.
There are many issues that are not covered by the holy Qur'an and the Sunnah. However, the Qur'an and the Sunnah provide the necessary guidelines to allow Muslims to come up with proper verdicts for any and all issues. Therefore, when a verdict about a certain issue is not found in the Qur'an or the Sunnah, the scholars of Islam research this issue and come up with the best possible verdict to make the life of Muslims easier and keeping in mind the best interest of the Islamic Ummah (Muslim community). One method used is Qiyas which uses analogies and comparison to derive Islamic legal rulings for new developments which were not present at the time of the prophet pbuh. For example if a guardian were to burn the property of an orphan there is no evidence that discusses this in the Quran however it would fall underthe same ruling as when the guardian spends the orphan’s wealth on himself. Allah says: “Lo! Those who devour the wealth of orphans wrongfully, they do but swallow fire into their bellies, and they will be exposed to burning flame.” [Surah al-Nisâ’: 10. Both acts bring loss to the orphan so they are both punished in the same way.
Muslim nations should strive to implement the Islamic Shariah in all matters. All laws, legislation, trade, politics and all other matters should be conducted according to the Shariah. Despite this no Muslim country actually currently follows the Shariah correctly. Instead many nations today rely in their so called "constitutions" on foreign systems of law. Many nations where the majority of inhabitants are Muslims derive their law from western systems of law, such as French or British law. This includes all matters including criminal law and even family law! The Quran states “And whoever does not judge by what Allah revealed, then they are Kafirun.”Surat Al-Maidah, Ayah 44. This practise of picking only some parts of God’s lawand abandoning the rest is not accepted in Islam. Justice is the ruling spirit of Islamic law, one of the main reasons for which the Prophet (peace be upon them all) were sent were to guide mankind to justice. In connection to this Allah, says, (We sent our messengers with clear signs and sent down with them the Book and the Balance so that men may conduct themselves with justice.” (Al-Hadid: 25) and “O you who believe, be upholders of justice, witnessing for Allah alone.) (An-Nisaa' 4: 135)
Changes in the world as well as the changing definition of concepts such as "civilized", "equality", "freedom", and "justice" have caused a critical light to shine upon Islamic laws. Such critics charge that the Shariah, in view of the changing world, is an outdated system of laws in need of amendment, replacement or abolishment. Views of this sort express rejection of divine guidance and reject that Allah has put us on this earth with a purpose in life and a set of rules to live by and achieve that purpose. To Muslims these rules are the ultimate criterion of justice and mercy and cannot nor need not be changed or measured against the changes and desires of society. Shariah law is fixed and rigid unlike western laws it does not grow and change with the circumstances of society, Shariah law controls society not the other way around.
According to Shariah law any offence, from assault to murder, that is committed against a person is to be punished by qisas which means retaliation. This is seen as a civil injury because the victim or their family have the right to prosecute and to choose compensation or diyah which is blood money instead of retaliation. This is similar to the famous “an eye for an eye, a tooth for a tooth. Islam, however, adds the following to such retribution it is better to forgive. In connection to this the Quran says “And the retribution for an evil act is an evil one like it, but whoever pardons and makes reconciliation - his reward is [due] from Allah . Indeed, He does not like wrongdoers” Quran 42:40
There are six crimes for which punishment is hadd (fixed): Apostasy, robbery, theft extramarital sex, unproven accusation of unchastely and drinking of an intoxicant. Punishments for these ranges from lashes to death, except for these crimes punishment is decided by the courts. When non Muslims hear of punishmentssuch as amputations of hands they generalise Shariah law as barbaric and medieval and suggest that it should be banned however these harsh punishments are only sent as deterrents and for any punishment to actually take place, proof must be provided, along with a confession of the crime or witnesses testifying against the criminal. If any of these is not sufficiently presented, Islamic law requires the hadd crime to be treated as a lesser crime. Similarly, if a thief could prove that he/she only stole because of need, then the Muslim society would be held at fault and made to supply that need and there would be no hadd punishment. Likewise, to be penalized for adultery, the couple had to be actually witnessed performing the physical act by four people who were in a position to identify both parties without doubt. This is why hardly anyone has actually been prosecuted because it would be impossible to provide such evidence.