Consider the process of teaching someone to cook rice. You wouldn’t initially throw them into a deep discussion about the variations among Fahrenheit, Celsius, and Kelvin. That would be like tossing them into a whirlpool of confusion. Instead, the initial focus should be on the essentials: how to proportion the rice and water, when to adjust the heat to a simmer, and the signs of perfectly cooked rice. As for knowing the temperature scales, this is not at the heart of cooking, although it is related to it. Take the foregoing as an example of teaching Usul al-Fiqh. Some scholars of Usul injected into the the study of this topic issues alien to it, preoccupying the minds of the new learners with things that cause them to come out of class having retained nothing of benefit with regards to Usul.

Along these lines, Abu Ishaq al-Shatibi, in the fourth introduction of Al-Muwafaqat, stated:

“Every issue mentioned in Usul al-Fiqh that does not serve as a foundation for subsidiary legal rulings, ethical conduct, or provide assistance in that regard, then placing them in Usul al-Fiqh is futile.”

Many of the linguistic, grammatical, and hadith-related disputes should be settled within that realm of specialized knowledge, not within the field of Usul. How many students of jurisprudence gain no understanding when studying this topic and instead are endlessly lost? Their journey in studying Usul yields no results, like a person who neither traveled far nor did his horse survive. Or perhaps with more modern language, like a person who throttles their engine and burns it out while their tires are stuck in the mud; their car is damaged and they don’t get anywhere.

Al-Shatibi here does not want you to exert immense effort in understanding matters that have no benefit or do not aid in achieving the greatest purpose of studying the principles of Usul, namely: to know what Allah and His Messenger want from us regarding specific cases.

The focus of scholars of principles on such matters is a waste of time and a diversion from the path of Allah. Why? Because the whole is not the sum of its parts. For example, the debate among Usul scholars regarding whether the knowledge of the Prophet (peace be upon him) was based on personal reasoning (ijtihad) or not. This matter – regardless of the theological implications behind it – is to be settled in the field of theology or the science of Islamic beliefs (‘ilm al-kalam) and not within the realm of Usul. Usul students should not be preoccupied with such matters because they do not serve as a foundation for action. The same can be said about purely linguistic and hadith-related issues as well.

Therefore, this principle – that the whole is not the sum of its parts – narrows the scope of knowledge within the field of Usul. Not everything related to Usul is necessarily an essential part of Usul itself. 

The following example may clarify this further: If you want to teach someone how to cook rice, you do not begin by teaching them the mechanisms of modern rice hulling and the engineering principles behind it. Although this may be related to a specific ingredient used when cooking (rice and how its produced), it is not suitable for a cooking lesson but rather an engineering class. Including it in a cooking lesson would be a waste of time, a foolish notion, or an arrogant display of dominance.

Hence, the principles of Usul are theoretical with respect to practical legal issues derived based on their foundations, but they are not theoretical in the sense that they delve into purely theoretical matters.