What is the concept of the human soul (nafs), and is it always prone to evil? And how does one deal with it?

The soul (ruh) and the self (nafs) are synonymous; they are what manage and move the body. When they depart from it, life leaves it, and they are from the command of Allah the Almighty. It is called nafs (self) in consideration of its management of the body, and ruh (soul) in consideration of its subtlety. Souls differ according to their owners and their environments: some incite to evil, some blame, and some are at peace. Psychological thoughts must be weighed against the Shari'a, and if they command evil, then they must be opposed.