Literally, Qiyas means measuring or ascertaining the length, weight, org quality of something.
It would be useful to start by giving a few examples.
To illustrate these, we might adduce the example of the Quran (al-maidah, 5;90), which explicitly forbids wine drinking. If this prohibition is to be extended by analogy to narcotic drugs, the four pillars of analogy in this example would be:
Far’ : taking drugs.
‘illah : the intoxicating effect.
Hukm : prohibition.
2. The hukm must be operative, which means that it has not been abrogated.
3. The hukm must be rational in the sense that the human intellect is capable of understanding the reason or the cause of its enactment, or that the ‘illah is clearly given in the text itself.
4. The fourth requirement concerning the hukm is that it must not be confined to an exceptional situation or to a particular state of affairs.
5. And lastly, the law of the text must not represent a departure from the general rules of qiyas in the first place.
2. The effective cause of analogy must be applicable to the new case in the same way as to the original case.
3. The application of qiyas to a new case must not result in altering the law of the text, for this would mean overruling the text by means of qiyas which is ultra vires.
2. As ready stated, the effective cause on which analogy is based must also be evident (zahir).
3. The third condation of ‘illah is that it must be a proper attribute (al-wasf al-munasib) in that it bears a proper and reasonable relationship to the law of the text (hukm).
4. The ‘illah must be ‘transient’ (muta’addi), that is, an objective quality which is transferable to other cases.
5. And finally, the effective cause must not be and attribute which runs counter to, or seeks to alter, the law of the text.