"The soul is the cause or source of the living body. The terms cause and source have many senses. But the soul is the cause of its body alike in all three senses which we explicitly recognize. It is (a) the source or origin of movement, it is (b) the end, it is (c) the essence of the whole living body" (Aristotle, De Anima).
What, if anything, constitutes the human "soul" is by no means universally agreed upon today. Some materialistic and other philosophers and scientists deem it illegitimate to ask such questions. Many deny it as a supra-bodily spiritual or metaphysical phenomenon. What is the `essence' of the human being, however, has for several thousand years been a subject of deep and constant religious and philosophical debate. For many centuries varieties of resolutions to this and related questions have occupied some of the greatest religious and scientific minds. For many today, when the quest for the nature and purpose of human life and the possibility of human immortality remain fundamental, such questions are of paramount importance. This paper will be a meditation upon select past ideas about the human mind-soul-intellect-spirit-essence along with a summary presentation of aspects of the Bahá'í position and its Graeco-Islamic background.
"O Kumayl [spirits] (anfus) are four  the augmentative vegetative [plant spirit] (al-namiyya al-nabatiyya)  the sensate animal [spirit] (al-hissiyya al-hayawaniyya)  the sacred rational (al-natiqa al-qudsiyya) [human spirit] and  the universal Divine [Spirit] (al-kulliyya al-ilahiyya)" (Attributed to Imam `Ali (d. 40/661) as cited in Majlisi, Bihar al-anwar, vol. 58:85)
"Know thou that the soul of man is exalted above, and is independent of all infirmities of body or mind ... The soul of man is the sun by which his body is illumined, and from which it draweth its sustenance, and should be so regarded" (Bahá'u'lláh, GWB: LXXX).
"... spirit is universally divided into five categories:  the vegetable spirit,  the animal spirit,  the human spirit,  the spirit of faith, and  the Holy Spirit ... The human spirit which distinguishes man from the animal is the rational soul, and these two namesthe human spirit and the rational souldesignate one thing ... But the mind is the power of the human spirit. Spirit is the lamp; mind is the light which shines from the lamp ... (`Abdu'l-Bahá', SAQ, LV).
It will be demonstrated in this paper that the roots of much religious thought on the question of the "soul" can be found in select Biblical texts and ancient in numerous Graeco-Islamic philosophical treatises. The massively influential Greek philosopher Aristotle (384-322 BCE) authored a well-known and foundational Greek treatise Î ÎµÏá½¶ Î¨Ï…Ï‡á¿†Ï‚ (= Peri Psyches, Latin = De Anima), "On the Soul" in which he gave an elaborate description of the functions of the soul. Many Jewish (e.g. Moses Maimonides), Christian (e.g. Tertullian of Carthage and Thomas Aquinas) and Muslim thinkers (see below) have been influenced by versions or translations of the De Anima and related works of Aristotle and other Hellenistic thinkers of antiquity.
Along with a large quantity of Greek philosophical writings, the De Anima of Aristotle was several times paraphrased and translated into Arabic. In `Abbasid times, the Christian Hunayn ibn Ishaq (d. 260/873) accomplished this as did Muslims and others associated with the circle of his erudite contemporary Ya`qub ibn Ishaq al-Kindi (d. c. 260/873). Matters were again taken up and developed by Abu Nasr Muhammad al-Farabi (d. 339/950) and by Abu `Ali al-Husayn ibn `Abd-Allah ibn Sina, better known in the west as Avicenna (d. 428/1037), an important philosopher, physician and mathematician whose massive, multi-volume Kitab al-shifa' (Book of the Cure) includes a Kitab al-nafs or `Treatise on the Soul'. Therein Islamic and Neoplatonic thought are integrated and developed. Among many others who contributed to the evolution of ideas about the soul was Fakhr al-Din al-Razi (d. 606/1209), who penned an important treatise entitled Kitab al-nafs wa'l-ruh wa sharh quwahuma (`The Book of the Soul and the Spirit and an exposition of their Faculties') and Ibn Rushd or Averroes (d. 595/1198), who wrote several important Arabic commentaries upon Aristotle's De anima. These Islamic philosophers respected and utilized but went way beyond Aristotle's foundational speculations in setting down their sophisticated ideas about the human soul-spirit-mind-intellect. Their thoughts contributed to the Bahá'í spiritual psychology mentioned in various scriptural writings or alwah ("Tablets") of Bahá'u'lláh and found, for example, in chapters of `Abdu'l-Bahá's Mufavaddat ("Some Answered Questions").
In the Arabic and Persian languages a spectrum of terms has sometimes interchangeably been used to pinpoint and define aspects of the human soul-spirit-mind-essence, etc; including, for example, rÃºh ("soul"-"spirit") , `aql (intellect) and nafs ("soul"). The last of these terms has a very rich Abrahamic (Semitic) religious semantic history being linked with the biblical Hebrew term nephesh "soul". When, according to Genesis 2:7, God created and breathed into the human (Adam), he became a nephesh hayya or "living soul". The Arabic-Persian word nafs, when linked with other words, has a very wide range of senses ranging from the lower, possibly satanic human "self" to that Logos-like Divine Reality, sometimes designated the nafs kulliyya or "Universal Soul".
In his commentary on the hadith "He who hath known his nafs ("Self") hath known his Lord" (man arafa nafsahu fa-qad `arafa rabbahu) and elsewhere, the great Shi`i philosopher theologian and mystic, Shaykh Ahmad al-Ahsa'i (d. 1246/1826) makes wide-ranging and detailed comments upon the meaning of the word nafs ("soul", etc), as does his successor Sayyid Kazim Rashti (d. 1259/1843) in a number of his books and treatises.
Despite the massive legacy of the past 2,500 years of thought about the human `soul' many still wonder whether and in what senses, if at all, one can legitimately speak of an individualized human "soul" (nafs), "spirit" (ruh), "mind" or "intellect" (aql). Bahá'í sacred writings have a good deal to say about these matters, making it perfectly clear, for example, that every individual, no matter of what religious or non-religious background, has had, from the moment of conception, an individualized eternal reality designated as the "soul". Exactly what this "soul" is remains something deeply mysterious, though deeply real by virtue of its potentialities and spiritual-intellectual capacities. For Bahá'ís the human "mind" with its spiritually related intellectual powers expresses aspects of the many perfections of the multi-faceted human soul. In this paper such questions will be considered and tentative conclusions drawn.