Is it permissible for me to exercise ijtihad in disputed religious matters, and to act upon it for myself, given my understanding of the hadiths and my memorization of many of them, without having memorized the Qur'an?

People are divided into three categories concerning ijtihad (independent reasoning in Islamic law): a knowledgeable mujtahid (qualified scholar), a distinguished student of knowledge, and a layperson.

The first: is qualified to perform ijtihad himself. The second: is a student of knowledge who has the ability to distinguish between different opinions and evidence. He may perform ijtihad in a specific area in which he has specialized; this is called "partial ijtihad," and it is the view of the majority. The third: is the layperson who imitates (follows) scholars and asks those he trusts. He is not able to perform ijtihad or examine the evidence.

Whoever has studied the Islamic sciences and possesses the ability to distinguish between the stronger and weaker opinions may examine the evidence and adopt what he deems stronger, knowing that preference (tarjih) depends on understanding the rules of language, jurisprudence, and its principles. Before reaching this stage, his ruling is that of a layperson. Memorizing some hadiths is not sufficient for preferring one opinion over another without comprehending their implications and authenticity. Absolute ijtihad is an advanced stage of knowledge, understanding, and deep immersion in the Islamic sciences, and few people reach it.