Terminology
In the writings of Muslim scholars, the term Nafs (self or soul) was used to denote individual personality and the term fitrah for human nature. Nafs encompassed a broad range of faculties including the qalb (heart), the ruh (spirit), the aql (intellect) and irada (will). Muslim scholarship was strongly influenced by Greek and Indian philosophy as well as by the study of scripture, drawing particularly from Hippocrates' understanding of the four humors of the body.
In medieval Islamic medicine in particular, the study of mental illness was a speciality of its own, and was variously known as al-‘ilaj al-nafs (approximately "curing/treatment of the ideas/soul/vegetative mind), al-tibb al-ruhani ("the healing of the spirit," or "spiritual health") and tibb al-qalb ("healing of the heart/self," or "mental medicine").
The Classical Arabic term for the mentally ill was "majnoon" which is derived from the term "Jinn", which is a spiritual being mentioned in the Quran which can either be good or evil in nature. It was originally thought that mentally ill individuals were possesed by these beings, however, due to their nuanced nature treatment on the mentally ill could not be generalized as it was in medieval Europe This term was gradually redefined among the educated, and was defined by Avicenna as "one who suffers from a condition in which reality is replaced with fantasy".
Read more about this topic: Psychology In Medieval Islam