still have self-consciousness. He thus concludes that the idea of the self is not logically dependent on any physical thing, and that the soul should In religion and philosophy, the soul is the immaterial aspect or essence of a living being. It is typically believed to be immortal and to exist apart from the material world. Anthropologists and psychologists have found that most humans believe in the existence of a soul or spirit, and that they have cross-culturally distinguished between the soul (or spirit) and the material body. Different reli Greek philosophers, such as Socrates, Plato, and Aristotle, understood that the soul (ψυχή, psykhḗ) must have a logical faculty, the exercise of which was the most divine of human actions. At… Following Aristotle, Avicenna (Ibn Sina) and Ibn al-Nafis, an Arab physician, further elaborated upon the Aristotelian understanding of the soul and developed their own theories on the soul. They both made a distinction between the soul and the spirit, and the Avicennian doctrine on the nature of the soul was influential among later Muslims. Some of Avicenna's views on the soul include 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. While he was imprisoned, Avicenna wrote his famous "Floating man" thought experiment to demonstrate human self-awareness and the substantial nature of the soul. He told his readers to imagine themselves suspended in the air, isolated from all sensations, which includes no sensory contact with even their own bodies. He argues that in this scenario one would still have self-consciousness. He thus concludes that the idea of the self is not logically dependent on any physical thing, and that the soul should not be seen in relative terms but as a primary given, a substance. This argument was later refined and simplified by René Descartes in epistemic terms, when he stated, "I can abstract from the supposition of all external things, but not from the supposition of my own consciousness." Avicenna generally supported Aristotle's idea of the soul originating from the heart, whereas Ibn al-Nafis rejected this idea and instead argued that the soul "is related to the entirety and not to one or a few organs". He further criticized Aristotle's idea whereby every unique soul requires the existence of a unique source, in this case the heart. Al-Nafis concluded that "the soul is related primarily neither to the spirit nor to any organ, but rather to the entire matter whose temperament is prepared to receive that soul", and he defined the soul as nothing other than "what a human indicates by saying "I"".