Consequently, Avicenna's ontology is 'existentialist' when accounting for being qua existence in terms of necessity ("wujub"), while it is 'essentialist' in terms of thinking about being qua existence ("wujud") in terms of contingency qua possibility ("imkan"; or "mumkin al-wujud": contingent being). Some argue that Avicenna anticipated Frege and Bertrand Russell in "holding that existence is an accident of accidents" and also anticipated Alexius Meinong's "view about nonexistent objects." He also provided early arguments for "a 'necessary being' as cause of all other existents." The idea of "essence precedes existence" is a concept which dates back to Avicenna and his school of Avicennism as well as Shahab al-Din Suhrawardi and his Illuminationist philosophy. The opposite idea of "existence precedes essence" was thus developed in the works of Averroes and Mulla Sadra's transcendent theosophy. More careful approaches are needed in terms of thinking about philosophers (and theologians) in Islam in terms of phenomenological methods of investigation in ontology (or onto-theology), or by way of comparisons that are made with Heidegger's thought and his critique of the history of metaphysics. Ibn al-Nafis wrote the "Theologus Autodidactus" as a defense of "the system of Islam and the Muslims' doctrines on the missions of Prophets, the religious laws, the resurrection of the body, and the transitoriness of the world." The book presents rational arguments for bodily resurrection and the immortality of the human soul, using both demonstrative reasoning and material from the hadith corpus as forms of evidence. Later Islamic scholars viewed this work as a response to Avicenna's metaphysical argument on spiritual resurrection (as opposed to bodily resurrection), which was earlier criticized by al-Ghazali. The Muslim physician-philosophers, Avicenna and Ibn al-Nafis, developed their own theories on the soul. They both made a distinction between the soul and the spirit, and in particular, the Avicennian doctrine on the nature of the soul was influential among the Scholastics. Some of Avicenna's views on the soul included the idea that the immortality of the soul is a consequence of its nature, and not a purpose for it to fulfill. In his theory of "The Ten Intellects", he viewed the human soul as the tenth and final intellect.