Usul fiqhda biror narsa manba sifatida ta'riflanadi, agar u yangi hukmlar (ahkom) uchun asos bo'lib xizmat qilsa. Qiyos manba hisoblanadi, chunki undan yangi ahkomlarni chiqarish mumkin. Asl hukmni "illat" (umumiy sabab) orqali yangi voqeliklarga kengaytirish yangi ahkomlarga olib keladi, shuning uchun qiyos manba hisoblanadi. Bu Islomning har zamon va har makonga tatbiq etilish qobiliyatini anglashning yo'llaridan biridir, chunki yangi voqeliklar va muammolar uchun ahkomlarni istinbot qilish mumkin.

Something is defined as a source in Usul when it serves as a source for new Ahkam (rules). Qiyas is a source because we can extract new Ahkam from it. By extending the original rule to new realities via a shared „Illah, leads to new Ahkam for new realities and hence Qiyas is a source. This is one of the ways we can appreciate the capacity of Islam to apply to all times and places as Ahkam can be deduced for new realities and problems.

Qiyos har doim quyidagi to'rt rukunga asoslanadi:

Qiyas is always built on the following four pillars:

I. Asl (eski masala).

i. Asl (old matter).

ii. Fari‟ (yangi masala).

ii. Fari‟ (new matter).

iii. Hukm (hukm).

iii. Hukm (rule).

iv. „Illah (ta'sir etuvchi sabab).

iv. „Illah (effective reason).

Masalan, Alloh (SWT) aytdi:

For example Allah (swt) said:

“Va ular uchun qo‘lingizdan kelgancha kuch va otliq qo‘shinlarni tayyorlab qo‘ying, shu bilan Allohning dushmanini va sizning dushmaningizni qo‘rqitasiz.”

“And make ready against them all you can of power including horses to threaten the enemy of Allah.” (TMQ Al-Anfal: 60)

Hukm, berilgan oyatda tayyorgarlik ko'rish farz ekanligidir. Eski masala otlardir. „Illat dushmani Allahning dushmanini qo'rqitishdir. Yangi masalaga kelsak, u tayyorgarlikning „illatini, ya'ni dushmanni qo'rqitishni amalga oshiradigan har qanday narsadir. Shu sababli bugungi kunda tanklar, jangovar samolyotlar va samolyot tashuvchi kemalarga ega bo'lish vojib bo'ladi, chunki ular dushmanni qo'rqitadi. Bundan tashqari, „illat Islom davlatini quyidagi sohalarda tayyorgarlik ko'rishga majbur qiladi:

The Hukm given in the verse is that preparation is an obligation. The old matter is horses. The „Illah is to terrify the enemy of Allah. As for the new matter, it is anything that will realise the „Illah of the preparation, which is to terrify the enemy. So these days it would be obligatory to have tanks, fighter planes, and aircraft carries since they terrify the enemy. Not only that, the „Illah obliges the Islamic State prepare in the following areas:

a) Agar u o‘z vazifasini bajarishi kerak bo‘lsa, qurol-yarog‘ rivojlantirish va harbiy sanoat o‘z davrining eng kuchlisi bo‘lishi shart, toki dushmanni qo‘rqitish „illati“ amalga oshsin.

a) The arms development and war industry must be the strongest of its age if it is to fulfill the „Illah of terrifying the enemy.

b) Davlat o‘z quvvat manbalari uchun boshqalarga bog‘liq bo‘la olmaydi, shuning uchun u o‘z qurol-yarog‘ini va jangovar vositalarini ishlab chiqishga intilishi lozim.

b) The state cannot depend on others for its sources of power and hence it has to strive to develop its own weapons and armaments.

c) U yangi, murakkab qurollarga ega bo‘lishi kerak, ular dushman qalbiga qo‘rquv solsin.

c) It should have new sophisticated weapons which will strike fear in the hearts of the enemy.

Usul al-Fiqh kitoblarida qiyosning o'ziga xos shartlari va talablari bayon etilgan. Ulardan biri shuki, yangi masala uchun Qur'on, Sunnat va sahobalar ijmosidan biron-bir mavjud hukm bo'lmasligi kerak.

There are specific guidelines and requirements for Qiyas explained in the books of Usul al-Fiqh. One such guideline is that there should be no existing ruling from the Qur‟an, Sunnah and Ijma‟ as-Sahabah for the new case.

Misol: Ayol Vudu olishdan oldin tirnoq lakini olishi shartmi? Ba'zi kishilar ayolning vudu olish uchun tirnoq lakini olishi shart emas, deb da'vo qilishadi va buni paypoqlar ustiga mash tortish hukmiga qiyos qilish bilan asoslashadi.

Example: Does a woman have to remove the nail polish before performing Wudhu? Some people claim she does not have to remove the nail polish in order to do Wudhu, and they justify it by doing Qiyas on the performance of Masah (wiping over the socks).

Qiyosni bu holatda qo'llab bo'lmaydi, chunki wudu haqidagi oyat qo'llarning barcha qismlarini yuvishni aniq buyuradi, lak esa suvning tirnoqlarga yetishiga to'sqinlik qiladi. Mash qilish (paypoqlar ustiga mash tortish) masalasida esa matnda illat (huquqiy sabab) keltirilmagan, shuning uchun uni boshqa narsalarga kengaytirib bo'lmaydi. Demak, bu masalada qiyosni qo'llash mumkin.

Qiyas cannot be performed in this situation because the Ayah regarding Wudhu explicitly orders to wash all parts of the hands, and polish prevents water from reaching the nails. In the case of Masah (wiping over the socks) the text is not presented with an „Illah (legal reason) and cannot be extended to other things. Thus, Qiyas can be practiced in this issue.

Qiyas uchun boshqa shartlardan biri shuki, asl hukm Qur'on, Sunnat va Ijmo' as-Sahoba'dan bo'lishi kerak, boshqa qiyosdan emas. Bundan tashqari, Qur'on, Sunnat va Ijmo' as-Sahoba matnlarida hukmning asosi (sababi) bo'lishi lozim. Biz sababni ('Illat) topish uchun o'z 'aql (aql-idrok)imizdan foydalana olmaymiz.

Some of the other requirements for Qiyas are that the original ruling has to be from Qur‟an, Sunnah and Ijma‟ as-Sahabah, not from another Qiyas. In addition, the texts of the Qur‟an, Sunnah and Ijma‟ as-Sahabah must contain the justification for the ruling. We cannot use our „Aql (intellect) to come up with the cause („Illah).