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In folk belief, spirit is the vital principle or animating force within all living things. As far back as 1628 and 1633 respectively, both William Harvey and René Descartes speculated that somewhere within the body, in a special locality, there was a ‘vital spirit’ or 'vital force', which animated the whole bodily frame, such as the engine in a factory moves the machinery in it.  Spirit has frequently been conceived of as a supernatural being, or non-physical entity; for example, a demon, ghost, fairy, or angel. In ancient Islamic terminology however, a spirit (rūḥ), applies only to pure spirits, but not to other invisible creatures, such as jinn, demons and angels.
Historically, spirit has been used to refer to a "subtle" as opposed to "gross" material substance, as put forth in the notable last paragraph of Sir Isaac Newton's Principia Mathematica. In English Bibles, "the Spirit" (with a capital "S"), specifically denotes the Holy Spirit.
The concepts of spirit and soul often overlap, and both are believed to survive bodily death in some religions, and "spirit" can also have the sense of ghost, i.e. a manifestation of the spirit of a deceased person. Spirit is also often used to refer to the consciousness or personality.
The modern English word "spirit" comes from the Latin spiritus, but also "spirit, soul, courage, vigor", ultimately from a Proto-Indo-European *(s)peis. It is distinguished from Latin anima, "soul" (which nonetheless also derives from an Indo-European root meaning "to breathe", earliest form *h2enh1-). In Greek, this distinction exists between pneuma (πνεῦμα), "breath, motile air, spirit," and psykhē (ψυχή), "soul" (even though the latter term, ψῡχή = psykhē/psūkhē, is also from an Indo-European root meaning "to breathe": *bhes-, zero grade *bhs- devoicing in proto-Greek to *phs-, resulting in historical-period Greek ps- in psūkhein, "to breathe", whence psūkhē, "spirit", "soul").
The word "spirit" came into Middle English via Old French. The distinction between soul and spirit also developed in the Abrahamic religions: Arabic nafs (نفس) opposite rūḥ (روح); Hebrew neshama (נְשָׁמָה nəšâmâh) or nephesh (נֶ֫פֶשׁ nép̄eš) (in Hebrew neshama comes from the root NŠM or "breath") opposite ruach (רוּחַ rúaħ). (Note, however, that in Semitic just as in Indo-European, this dichotomy has not always been as neat historically as it has come to be taken over a long period of development: Both נֶ֫פֶשׁ (root נפשׁ) and רוּחַ (root רוח), as well as cognate words in various Semitic languages, including Arabic, also preserve meanings involving miscellaneous air phenomena: "breath", "wind", and even "odour".)
"Spirit" has acquired a number of meanings:
- Christian theology can use the term "Spirit" to describe the Holy Spirit.
- Christian Science uses "Spirit" as one of seven synonyms for God, as in: "Principle; Mind; Soul; Spirit; Life; Truth; Love"
- Latter Day Saint prophet Joseph Smith Jr. taught that the concept of spirit as incorporeal or without substance was incorrect: "There is no such thing as immaterial matter. All spirit is matter, but it is more fine or pure, and can only be discerned by purer eyes." Regarding the soul, Joseph Smith wrote "And the Gods formed man from the dust of the ground, and took his spirit (that is, the man’s spirit), and put it into him; and breathed into his nostrils the breath of life, and man became a living soul." Thus, the soul is the combination of a spirit with a body (although most members use "soul" and "spirit" interchangeably). In Mormon scripture, spirits are sometimes referred to as "intelligences". But other Mormon scriptures teach that God organized the spirits out of a pre-existing substance called "intelligence" or "the light of truth". While this may seem confusing, it can be compared to how a programmer writes an algorithm by organizing lines of logical code. The logic always existed, independent of the programmer, but it is the creator who organizes it into a living spirit / intelligence / soul.
- Various forms of animism, such as Japan's Shinto and African traditional religion, focus on invisible beings that represent or connect with plants, animals, or landforms (kami): translators usually employ the English word "spirit" when trying to express the idea of such entities.
- According to C. G. Jung (in a lecture delivered to the literary Society of Augsburg, 20 October 1926, on the theme of “Nature and Spirit”):
The connection between spirit and life is one of those problems involving factors of such complexity that we have to be on our guard lest we ourselves get caught in the net of words in which we seek to ensnare these great enigmas. For how can we bring into the orbit of our thought those limitless complexities of life which we call "Spirit" or "Life" unless we clothe them in verbal concepts, themselves mere counters of the intellect? The mistrust of verbal concepts, inconvenient as it is, nevertheless seems to me to be very much in place in speaking of fundamentals. "Spirit" and "Life" are familiar enough words to us, very old acquaintances in fact, pawns that for thousands of years have been pushed back and forth on the thinker's chessboard. The problem must have begun in the grey dawn of time, when someone made the bewildering discovery that the living breath which left the body of the dying man in the last death-rattle meant more than just air in motion. It can scarcely be an accident onomatopoeic words like ruach (Hebrew), ruch (Arabic), roho (Swahili) mean ‘spirit’ no less clearly than πνεύμα (pneuma, Greek) and spiritus (Latin).
- Psychical research, "In all the publications of the Society for Psychical Research the term ‘spirit’ stands for the personal stream of consciousness whatever else it may ultimately be proved to imply or require" (James H. Hyslop, 1919).
Similar concepts in other languages include Greek pneuma, Chinese Ling and hun (靈魂) and Sanskrit akasha / atman (see also prana). Some languages use a word for spirit often closely related (if not synonymous) to mind. Examples include the German Geist (related to the English word ghost) or the French l'esprit. English versions of the Bible most commonly translate the Hebrew word ruach (רוח; wind) as "the spirit", whose essence is divine.
Alternatively, Hebrew texts commonly use the word nephesh. Kabbalists regard nephesh as one of the five parts of the Jewish soul, where nephesh (animal) refers to the physical being and its animal instincts. Similarly, Scandinavian, Baltic, and Slavic languages, as well as Chinese (气 qi), use the words for breath to express concepts similar to "the spirit".
- Daemon (classical mythology)
- Great Spirit or Wakan Tanka is a term for the Supreme Being.
- Philosophy of religion
- Shen (Chinese religion)
- Soul dualism
- Sprite (folklore)
- Spirit world (Latter Day Saints)
- Spirit world (Spiritualism)
- Michels, John (January 18, 1884). Science: Volume 3. Highwire Press, Jestor: American Association for the Advancement of Science. p. 75. https://books.google.com/?id=0IECAAAAYAAJ&pg=PA75&lpg=PA75&dq=scientist+who+believe+that+the+vital+force+within+all+living+things+is+spirit#v=onepage&q=scientist%20who%20believe%20that%20the%20vital%20force%20within%20all%20living%20things%20is%20spirit&f=false. Retrieved 10 October 2019.
- François 2009, p.187-197.
- Chodkiewicz, M., “Rūḥāniyya”, in: Encyclopaedia of Islam, Second Edition, Edited by: P. Bearman, Th. Bianquis, C.E. Bosworth, E. van Donzel, W.P. Heinrichs. Consulted online on 18 November 2019 <http://dx.doi.org/10.1163/1573-3912_islam_SIM_6323> First published online: 2010
- Burtt, Edwin A. (2003). Metaphysical Foundations of Modern Physical Science. Mineola, New York: Dover Publications, Inc. p. 275.
- OED "spirit 2.a.: The soul of a person, as commended to God, or passing out of the body, in the moment of death."
- anə-, from *ə2enə1-. Watkins, Calvert. 2000. The American Heritage Dictionary of Indo-European Roots, second edition. Boston: Houghton-Mifflin Co., p.4. Also available online. (NB: Watkins uses ə1, ə2, ə3 as fully equivalent variants for h1, h2, h3, respectively, for the notation of Proto-Indo-European laryngeal segments.)
- bhes-2. Watkins, Calvert. 2000. The American Heritage Dictionary of Indo-European Roots, second edition. Boston: Houghton-Mifflin Co., 2000, p.11. Also available online
- Koehler, L., Baumgartner, W., Richardson, M. E. J., & Stamm, J. J. (1999). The Hebrew and Aramaic lexicon of the Old Testament (electronic ed.) (711). Leiden; New York: E.J. Brill.
- Brown, F., Driver, S. R., & Briggs, C. A. (2000). Enhanced Brown-Driver-Briggs Hebrew and English Lexicon (electronic ed.) (659). Oak Harbor, WA: Logos Research Systems. (N.B. Corresponds closely to printed editions.)
- Brown, F., Driver, S. R., & Briggs, C. A. (2000). Enhanced Brown-Driver-Briggs Hebrew and English Lexicon (electronic ed.) (924ff.). Oak Harbor, WA: Logos Research Systems. (N.B. Corresponds closely to printed editions.)
- Eddy, Mary Baker (1875). "Glossary" (txt). Science and Health With Key to the Scriptures. p. 587. http://www.gutenberg.org/dirs/etext02/shkts11.txt. Retrieved 2009-03-11. "GOD — The great I AM; the all-knowing, all-seeing, all-acting, all-wise, all-loving, and eternal; Principle; Mind; Soul; Spirit; Life; Truth; Love; all substance; intelligence."
- Doctrine and Covenants 131:7
- "Abraham 5:7". https://www.churchofjesuschrist.org/study/scriptures/pgp/abr/5.7?lang=eng&clang=eng#p7.
- "Abraham 3:22". https://www.churchofjesuschrist.org/study/scriptures/pgp/abr/3.22?lang=eng&clang=eng#p22.
- "Topical Guide: Intelligence, Intelligences". https://www.churchofjesuschrist.org/study/scriptures/gs/intelligence-intelligences?lang=eng.
- Jung, C. G. (1960). "Spirit and Life". The Collected Works of C. G. Jung. XX. 8. New York, NY: Pantheon Books for Bollinger. pp. 319–320.
- Hyslop, James Hervey (1919). Contact with the Other World (First ed.). New York, NY: The Century Co.. p. 11. https://archive.org/details/contactwithother01hysl.
- "Ruach: Spirit or Wind or ???". http://www.biblicalheritage.org/Bible%20Studies/ruach.htm.
- François, Alexandre (2008), "Semantic maps and the typology of colexification: Intertwining polysemous networks across languages", in Vanhove, Martine, From Polysemy to Semantic change: Towards a Typology of Lexical Semantic Associations, Studies in Language Companion Series, 106, Amsterdam, New York: Benjamins, pp. 163–215, https://www.academia.edu/846905
- Baba, Meher (1967). Discourses. San Francisco: Sufism Reoriented. ISBN 1-880619-09-1. http://www.discoursesbymeherbaba.org.