Imam Ibn Al-Qayyim wrote in his scholarly work "Kitab al Ruh",

"Ruh {spirit} is an entity which differs totally from the physical body. It is a subtle, ecclesiastical, enlightened living and moving body which penetrates into the depths of the organs and flows into them like the water in the rose or the oil in the olive or the fire in the coal. As long as these organs remain able to accept the impressions of this subtle body, the 'Ruh' remains attached to these organs and provides them with feeling and movement. But when these organs are spoiled because of the dominance of diseased elements upon it, and they are no longer able to accept the impressions of the soul, it leaves the body and heads towards the world of the souls. "

There is some difference in the way the words 'Ruh' and 'Nafs' are used. The 'Ruh' is the subtle spirit, which resides in the heavens and needs a physical body to carry it on the earth. When this spirit is given a body, life begins and it is described as 'Nafs'. The word 'Nafs' is used in a number of ways by the Qur'an, all of which imply the meaning of a soul with a body.

'Nafs' meaning "Self."