The following is the draft english translation from the Usul Al-Fiqh masterpiece of the Arabic book الشخصية الاسلاميَة الجزء الثالث (The Islamic Personality Volume 3 ) by Sheikh Taqiuddin an-Nabhani. Please refer to the original Arabic for accurate meanings.
Chapter 1: Principles of Al Fiqh (Usul Al-Fiqh)
Linguistically ‘asl is that which can be constructed upon, whether the construction is tangible, like building a wall upon a foundation, or the construction can be rational, like building the reasoned rule (ma`lul) upon the legal reason (`illah) and like building a verdict (madlul) upon its evidence (dalil). So usul al-fiqh are the principles (qawa`id) upon which the fiqh is built. As for fiqh (jurisprudence), linguistically it refers to understanding (fahm); as in the saying of Allah (SWT):
مَا نَفْقَهُ كَثِيرًا مِمَّا تَقُولُ
“we don’t understand much of what you say….” [Hud: 91]
and in the terminology of jurists it refers to the knowledge of the practical shara' rules (which are) extracted from the detailed evidences. What is meant by “the knowledge of the rules” by the scholar (`alim) who knows them is not only mere knowledge, but having proficiency of the shar'i rules, i.e. this knowledge should deepen to the extent that the scholar acquires proficiency in these rules. Acquiring such proficiency is enough to consider the one who has it a scholar (faqeeh), even if he does not know all the ahkam.
However, it is a necessary for him to know a collection of the shar`i rules of the branches (fourou'iah) through deliberation/research (nadhar) and deduction/evidencing (istidlal). Accordingly, the knowledge of one or two rules is not called fiqh, nor can the knowledge that a kind of evidence is a proof be called fiqh. The term fiqh is used to mean the sum of the shar'i practical rules that are extracted from the detailed evidence. Thus when it is said that “this is a fiqh book”, it means that this is a book that contains practical rules of the branches; when it is said “the knowledge of fiqh”, it means the knowledge in the sum of the practical rules of the branches.
Importantly this is exclusive to the practical rules, because by the conventional definition, rules to do with belief (ahkam al-i`tiqadi) are not considered part of fiqh, because fiqh is particular to the practical rules (ahkam) of the branhces, i.e. the rules on which the actions are based, not beliefs.
Therefore the meaning of usul al-fiqh is the principles (qawa`id) upon which the acquisition of the proficiency in the practical rules that are extracted from the detailed evidences is built. Hence usul al fiqh is defined conventionally as the knowledge of the principles whereby the extraction (istinbat) of the shara' rules from the detailed evidences is attained; and these principles themselves are also termed usul al-fiqh. A book of usul al-fiqh means a book that contains these principles. So when it is said “the science of usul al fiqh”, it refers to the foundations by which the extracting of shar`i rules from the detailed evidences is achieved.
Accordingly the study of usul al-fiqh is a study of the principles, the evidences, i.e. a study of the rule, the sources of the rule, and in the method of extracting the rule from these sources. Usul al-fiqh includes the general evidences (adillah ijmaliyyah) and what they indicate, and it also includes, the situation of the one doing the deduction (mustadil) in general and not in details; i.e. (it includes) the knowledge of ijtihad (deriving rules), and the method of istidlaal (seeking the evidence), and the harmonising (ta`aadul) and giving preference (tarjih) between the evidences. As for ijtihad and the outweighing between evidences(tarjih) it depends on knowing the evidences and what these evidences indicate. Therefore these two studies: the evidences, and what these evidences indicate, are the foundations of usul al-fiqh, together with the study of the rule and matters that relate to it (the rule).
Thus, usul al-fiqh is the unspecified general evidences for, like the unrestricted/absolute command (mutlaq al-`amr) and unrestricted prohibition (mutlaq al-nahy), the actions of the Prophet (saw), the consensus of the companions and qiyas (analogy). Thus the detailed evidences are excluded from this, like Allah's (swt) saying: “and established the prayer”, “and do not come near fornication”, the prayer of the Messenger (saw) inside the ka'abah, the establishment of guardianship over the incompetent (al mahjour), and the deserving of the representative (wakil) to wages when hired on the basis of analogy to the payment of an employee. Finding them used as examples in the study of usul al-Fiqh does not mean thay are part of it. Nay, usul al-fiqh is the general evidences, what the evidences indicate, the state of the one evidencing, and the methodology of the evidencing (istidlal).
Usul al fiqh differs from the science of fiqh in that the subject of fiqh is the actions of the servants with regard to them being allowed (halaal), prohibited, valid, invalid and void. As for usul al-fiqh, its subject is the textual evidences (adiillah sam'iyah) with regards to the shar'i verdicts being derived from them, i.e. with regards to how they establish the shar`i verdicts. Thus it is necessary (in studying usul al-fiqh) to study the verdict and that which is related to it with regards to the explanation of who is it that issues the verdict, i.e. who has the right to issue the verdict: who is the legislator, and with regards to upon whom does the verdict apply, i.e who is responsible for executing the verdict, meaning, the one upon whom the verdict is obligated (mahkum `alayh), and with regard to the verdict itself: what is it, and what is its reality? After this comes the explanation of the evidences and what these evidences indicate.