One view is that it is obligatory and that knowledge depends upon it, as these people maintain.

Another view is that knowledge can be attained without it, but that it offers another path to knowledge. This is held by many who consider this method valid but do not regard it as obligatory, such as al-Khattābī, Judge Abū Yaʿlā, and Abū Jaʿfar al-Simnānī, the judge of Mosul and teacher of Abū al-Walīd al-Bājī. Al-Simnānī used to say: “Making rational inquiry obligatory is a remnant of Muʿtazilism that remained with Shaykh Abū al-Hasan al-Ashʿarī.”

These are the people who do not regard this particular rational inquiry as obligatory. Some of them do not regard rational inquiry as obligatory at all, such as al-Simnānī, Ibn Hazm, and others. Others regard it as obligatory in general, such as al-Khattābī and Abū al-Faraj al-Maqdisī. Judge Abū Yaʿlā sometimes adopts one position and sometimes the other; indeed, at times he even maintains that this particular form of inquiry is obligatory, as do Abū al-Maʿālī and others.

Among those who consider rational inquiry obligatory, some say that it is the first obligation. Others say: “Rather, it is the knowledge that must be attained through it.” This is a merely verbal dispute.

Similarly, some have said that the first obligation is the intention to undertake rational inquiry, as expressed by Abū al-Maʿālī. Others among them have said: “Rather, it is the doubt that precedes it,” as Abū Hāshim maintained. These and other views have been discussed at length elsewhere.