is sometimes considered to exhibit lack of continuity, absence of any chronological or thematic order and repetitiousness. Michael Sells, citing the work of the critic Norman O. Brown, acknowledges Brown's observation that the seeming disorganization of Quranic literary expression—its scattered or fragmented mode of composition in Sells's phrase—is in fact a literary device capable of delivering profound effects as if the intensity of the prophetic message were shattering the vehicle of human language in which it was being communicated. Sells also addresses the much-discussed repetitiveness of the Quran, seeing this, too, as a literary device. A text is self-referential when it speaks about itself and makes reference to itself. According to Stefan Wild, the Quran demonstrates this metatextuality by explaining, classifying, interpreting and justifying the words to be transmitted. Self-referentiality is evident in those passages where the Quran refers to itself as revelation (), remembrance (dhikr), news (), criterion () in a self-designating manner (explicitly asserting its Divinity, "And this is a blessed Remembrance that We have sent down; so are you now denying it?"), or in the frequent appearance of the "Say" tags, when Muhammad is commanded to speak (e.g., "Say: 'God's guidance is the true guidance'," "Say: 'Would you then dispute with us concerning God?'"). According to Wild the Quran is highly self-referential. The feature is more evident in early Meccan suras. Interpretation The Quran has sparked much commentary and explication (), aimed at explaining the "meanings of the Quranic verses, clarifying their import and finding out their significance." Tafsir is one of the earliest academic activities of Muslims. According to the Quran, Muhammad was the first person who described the meanings of verses for early Muslims. Other early exegetes included a few Companions of Muhammad, such as Abu Bakr, 'Umar ibn al-Khattab, 'Uthman ibn 'Affan, ʻAli ibn Abi Talib, 'Abdullah ibn Mas'ood, ʻAbdullah ibn Abbas, Ubayy ibn Kaʻb, Zayd ibn Thaabit, Abu Moosaa al-Ash’ari, and ‘Abdullah ibn al-Zubayr. Exegesis in those days was confined to the explanation of literary aspects of the verse, the background of its revelation and, occasionally, interpretation of one verse with the help of the other. If the verse was about a historical event, then sometimes a few traditions (hadith) of Muhammad were narrated to make its meaning clear. Because the Quran is spoken in classical Arabic, many of the later converts to Islam (mostly non-Arabs) did not always understand the Quranic Arabic,