After Muhammad’s death, leaders who claimed authority over the entire Muslim community took the title of caliph (literally “successor”) until 1924. In practice, Muslims splintered over how to choose the caliph and what his role should be: tribal shaykh, imperial ruler, or supreme religious authority. This debate continues to shape opposing notions of an Islamic state today.

After Muhammad’s death, Muslims collected “traditions” (hadith) of what Muhammad said or did and viewed these as authoritative for resolving religious questions. Reza Aslan argues that the hadith are often inaccurate, that their authority stifles the creativity of the early Ulama, and that many were invented to legitimize later inequalities. His Islamic Reformation can only progress by evaluating the hadith critically.

Ijtihad is a term in Islamic legal jurisprudence for determining new principles based solely on one’s own reasoning rather than starting with an authority (such as the Quran or hadith). Aslan argues that ijtihad’s gradual restriction by clerical institutions is one of the major problems hindering Islam’s development.