[Principles of Religion and Principles of Jurisprudence according to the Zaydiyyah]

I answered with an oral answer in a public gathering, and the summary of the answer was:
1- That this is a false propaganda intended to turn people away from studying these two sciences and to distance them from knowing the rulings of Allah, Exalted is He, with which He charged His servants, namely:
a) doctrinal rulings (the principles of religion),
b) practical rulings (acts of worship and transactions). And knowing these properly depends upon knowing the principles of jurisprudence.
2- The one who laid the foundations of the science of the principles of religion and the science of the principles of jurisprudence is Imam ʿAlī ibn Abī Ṭālib (Peace be Upon Him). Whoever wishes to know the soundness of what we have mentioned should consult the book Nahj al-Balāghah, which contains much of the speech, sermons, letters, and wisdom of the Commander of the Faithful ʿAlī (Peace be Upon Him), and the book Sharḥ Nahj al-Balāghah by Ibn Abī al-Ḥadīd, for he will find therein confirmation of what we have stated.
This is in addition to the fact that the scholars of the Muʿtazilah attribute the science of the principles of religion to the Commander of the Faithful ʿAlī (Peace be Upon Him) through their connected chains of transmission to al-Ḥasan ibn Muḥammad ibn ʿAlī ibn Abī Ṭālib, from his father, from his grandfather.
And ʿAlī ibn Abī Ṭālib (Peace be Upon Him) mentioned all the chapters of the principles of jurisprudence in Nahj al-Balāghah, and he (Peace be Upon Him) mentioned therein the conditions of narrators, which is the foundation of the science of ḥadīth.
3- Imam Zayd ibn ʿAlī (Peace be Upon Him) has books and epistles in the science of the principles of religion, printed within the collected works of Imam Zayd ibn ʿAlī, in which he mentioned the greatest chapters of the principles of religion. The books of Imam Zayd ibn ʿAlī ere among the earliest works compiled and written in Islam, and the Muʿtazilah at his time had no books or writings; rather, the Muʿtazilah had not yet been born nor come into existence.
4- The science of the principles of religion exists in its entirety in the Noble Qur’an, from its beginning to its end. The reason for the disagreement of Muslim scholars in many of the principles of religion is their disagreement in interpreting the clear (muḥkam) and the ambiguous (mutashābih) of the Qur’an. Their disagreement arises either from differences in understanding or from inclinations of desire.
5- The science of the principles of jurisprudence also exists potentially within the Wise Qur’an, for the Qur’an contains the general and the specific, the absolute and the restricted, the concise and the elaborated, the explicit text and the apparent and the interpreted, the expressed meaning and the implied meaning, the literal and the metaphorical, the clear and the ambiguous, command and prohibition, abrogating and abrogated, concession and strict rule, individual obligation and collective obligation, specified obligation and optional obligation, absolute and time-bound, restricted and expansive, performance and make-up, ijtihād and taqlīd, and that the Qur’an is a proof, and that the statements, actions, and omissions of the Prophet (May Allah bless him and his family and grant them peace) are a proof, etc.
- The student of the Qur’an, even if he reaches the utmost degree of intelligence, acumen, and memorization, cannot, by his intelligence and acumen alone, reach the intent of Allah, Exalted is He, regarding the rulings with which Allah charged His servants, unless he has firm grounding in the knowledge of the principles of jurisprudence; otherwise, he will stumble in his understanding and stray far from the intended meaning.
6- The science of the principles of jurisprudence is not sought for its own sake; rather, it is an instrument by which one reaches knowledge of the rulings of the Qur’an and the Sunnah. It may be likened to a lens that reveals and clarifies what cannot be clearly seen by the naked eye.
7- If the science of the principles of jurisprudence were from the sciences of the Ashʿariyyah, all the other schools would not have accepted it from them, such as the Imāmiyyah, the Zaydiyyah, the Salafiyyah, the Ẓāhiriyyah, and the Ibāḍiyyah. Likewise, if the science of the principles of religion were from the sciences of the Muʿtazilah, the other sects—such as the Imāmiyyah, the Zaydiyyah, the Ibāḍiyyah, etc.—would not have accepted it, due to the enmity between them.
8- There is no doubt that Muslim scholars differed regarding divine doctrines. Some of them said that the legally responsible person is free in his actions, whether obedience or disobedience; and some of them said rather that the servant has no action in obedience or disobedience, nor any will therein, but that Allah, Exalted is He, is the One who performs obedience and disobedience in the servant by His power, will, and decree. These differences were debates in which each group presented what it could of proofs and arguments, and each group attempted to invalidate what the other group presented of proofs and evidences.
9- Likewise were the disagreements among Muslim scholars in the rest of the divine sciences. Those disagreements, along with the proofs, evidences, doubts, rebuttals, and answers involved in them, were written down, because of the insight they give to the observer, the strengthening of knowledge of truth over falsehood, and the reassurance of the soul—such that no one can mislead the student regarding his religion or confuse him regarding his beliefs.
- Knowledge in all its types is praiseworthy and good to learn, and its bearer is praised, including the science of the principles of religion and the science of the principles of jurisprudence—except for the science of magic, the science of astrology, and the science of soothsaying. The scholars of the Muslims, from all sects, have not differed on this throughout Islamic history until today. Therefore, there is no consideration for the condemnation of those who condemn these two sciences, nor any weight to their blame, for it contradicts the consensus of the Muslims—rather, the consensus of the majority of the scholars.
- I have also heard from others besides this questioner that these two sciences are misguidance, and they justify that by claiming that they are not from the sciences of the Ahl al-Bayt, but rather from the science of the Muʿtazilah and the science of the Ashʿariyyah.
Among their justifications is that the science of the principles of jurisprudence is a cause of people’s disagreement, in that within the science of the principles of jurisprudence there is a rule which states: “Every mujtahid among the scholars is correct.” This rule, according to them, justifies disagreement, encourages it, deems it correct, and admits it into the truth—despite the fact that Allah, Exalted is He, has forbidden division and disagreement in the Qur’an.
The response to this justification is that it was incumbent upon them to direct their criticism to this rule alone, and not to generalize their criticism to everything contained in the science of the principles of jurisprudence. This is the logical principle followed by scholars.
- What is meant by that rule among Muslim scholars is the validation of the mujtahids regarding the matters in which they exercised ijtihād for issues whose rulings are not explicitly stated by a text from the Book, nor from the Sunnah, nor from those upon whom consensus has been established—such as newly emerging issues that did not occur in the time of the Messenger (May Allah bless him and his family and grant them peace) but arose later or in our time. Examples of this include:
1. One who travels by air from China to Yemen after having prayed ẓuhr and ʿaṣr there, then arrives at Sanaʿa airport before the time of ẓuhr for that day has entered—does he have to pray ẓuhr and ʿaṣr again when the time enters, or not?
2. How does a Muslim pray the five daily prayers in the Arctic Circle, where the sun may rise and then set after minutes, or remain shining and then set briefly, then rise again, depending on the seasons there?
3. Buying and selling by means of the telephone.
4. Dissecting corpses in medical colleges, or for determining the cause of death.
5. Do intravenous nutrition and injections invalidate the fast?
6. Is a person suffering from asthma required to make up the fast if he uses an inhaler?
7. What is the legal ruling regarding what various insurance companies do?
Such issues require the consideration of the mujtahids to derive their rulings from the sources of legislation.

Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.3