The astrophysicist Nidhal Guessoum while being highly critical of pseudo-scientific claims made about the Quran, has highlighted the encouragement for sciences that the Quran provides by developing "the concept of knowledge.". He writes: "The Qur'an draws attention to the danger of conjecturing without evidence (And follow not that of which you have not the (certain) knowledge of... 17:36) and in several different verses asks Muslims to require proofs (Say: Bring your proof if you are truthful 2:111), both in matters of theological belief and in natural science." Guessoum cites Ghaleb Hasan on the definition of "proof" according the Quran being "clear and strong... convincing evidence or argument." Also, such a proof cannot rely on an argument from authority, citing verse 5:104. Lastly, both assertions and rejections require a proof, according to verse 4:174. Ismail al-Faruqi and Taha Jabir Alalwani are of the view that any reawakening of the Muslim civilization must start with the Quran; however, the biggest obstacle on this route is the "centuries old heritage of tafseer (exegesis) and other classical disciplines" which inhibit a "universal, epidemiological and systematic conception" of the Quran's message. The philosopher Muhammad Iqbal, considered the Quran's methodology and epistemology to be empirical and rational.