Pre-existence, preexistence, beforelife, or premortal existence refers to the belief that each individual human soul existed before mortal conception, and at some point before birth enters or is placed into the body. Concepts of pre-existence can encompass either the belief that the soul came into existence at some time prior to conception or the belief that the soul is eternal. Alternative positions are traducianism and creationism, which both hold that the individual human soul does not come into existence until conception. It is to be distinguished from preformation, which is about physical existence and applies to all living things. Ancient Greek thought and Islam affirm pre-existence, but it is generally denied in Christianity.
Plato believed in the pre-existence of the soul, which tied in with his innatism. He thought that we are born with knowledge from a previous life that is subdued at birth and must be relearned. He saw all attainment of knowledge not as acquiring new information, but as remembering previously known information. Before we were born, we existed in a perfect world where we knew everything.
A concept of pre-existence was advanced by Origen, a second and third-century church father. Origen believed that each human soul was created by God at some time prior to conception. Church Fathers Tertullian and Jerome held to traducianism and creationism, respectively, and pre-existence was condemned as heresy in the Second Council of Constantinople in AD 553.
Origen quoted Romans 9:11-14 as evidence for his position:
For the children being not yet born, neither having done any good or evil, that the purpose of God according to election might stand, not of works, but of him that calleth; It was said unto her, The elder shall serve the younger. As it is written, Jacob have I loved, but Esau have I hated. What shall we say then? Is there unrighteousness with God? God forbid.
Origen argued that God could not love Jacob and hate Esau until Jacob had done something worthy of love and Esau had done something worthy of hatred, therefore, this passage only means that Jacob and Esau had not yet done good or evil in this life and their conduct before this life was the reason why Esau would serve Jacob. He rejected the position that God loves or hates a soul based on its inclination toward good or evil, before the soul actually commits a good or evil act. (God, being the creator of all souls and their inclinations, knows perfectly well each soul's inclination toward good or evil.)
Origen also quoted Jeremiah 1:5:
Before I formed thee in the belly I knew thee; and before thou camest forth out of the womb I sanctified thee, and I ordained thee a prophet unto the nations.
Those who reject pre-existence, which would be every Christian denomination that accepts the conclusions of the Second Council of Constantinople (i.e., all Catholics and Eastern Orthodox Christians and many Protestants), simply see Jeremiah 1:5 as another passage about God's foreknowledge. This ecumenical Council explicitly stated "If anyone asserts the fabulous pre-existence of souls, and shall assert the monstrous restoration which follows from it: let him be anathema." This would make rejection of Origen's doctrine likely to be the majority Christian opinion to the present day.
The belief that human souls choose good or evil totally independently of God's will, which is most often found among the more extreme Arminian Christians, means that God does not ultimately determine the will of each soul. However, ex nihilo creation, a belief also commonly found among Arminians, means that God determined everything that exists, including the will of each soul, without drawing on anything but himself. The question is definitively resolved in Calvinism by asserting that all souls act according to God's sovereign will, and in Mormonism (see below) by asserting that human souls have always existed and are co-eternal with God.
The concept of premortal existence is an early and fundamental doctrine of Mormonism. In 1833, early in the Latter Day Saint movement, its founder Joseph Smith taught that human souls are co-eternal with God the Father just as Jesus is co-eternal with God the Father, "Man was also in the beginning with God. Intelligence, or the light of truth, was not created or made, neither indeed can be."
In 1844, Smith elaborated on this idea in his King Follett discourse:
...the soul—the mind of man—the immortal spirit. Where did it come from? All learned men and doctors of divinity say that God created it in the beginning; but it is not so: the very idea lessens man in my estimation...We say that God Himself is a self-existing being...Man does exist upon the same principles...[The Bible] does not say in the Hebrew that God created the spirit of man. It says, "God made man out of the earth and put into him Adam's spirit, and so became a living body." The mind or the intelligence which man possesses is co-equal with God himself...Is it logical to say that the intelligence of spirits is immortal, and yet that it has a beginning? The intelligence of spirits had no beginning, neither will it have an end. That is good logic. That which has a beginning may have an end. There never was a time when there were not spirits; for they are co-equal with our Father in heaven.
In the context of this core LDS doctrine, the term premortal existence is a significantly more accurate term to describe the time before this mortal existence than pre-existence, since pre-existence has a connotation of something existing before the beginning of existence, and LDS doctrine specifically rejects ex-nihilo creation. Therefore, the term "premortal existence" is strongly preferred in the LDS church to represent the time before this mortal life, however the term "pre-existence" is in widespread use.
After Smith's death, the doctrine of premortal existence was elaborated by some other leaders within The Church of Jesus Christ of Latter-day Saints (LDS Church). Although the mind and intelligence of humanity were still considered to be co-eternal with God, and not created, Brigham Young introduced the idea that the spirit, which he distinguished from the mind or intelligence, was indeed created and not co-eternal with God. Young postulated that we each had a pre-spirit intelligence that later became part of a spirit body, which then eventually entered a physical body and was born on earth. In 1857, Young stated that every person was "a son or a daughter of [the Father]. In the spirit world their spirits were first begotten and brought forth, and they lived there with their parents for ages before they came here."
In the LDS Church the idea of spirit birth was described in its modern doctrinal form in 1909, when the church's First Presidency issued the following statement:
Jesus, however, is the firstborn among all the sons of God—the first begotten in the spirit, and the only begotten in the flesh. He is our elder brother, and we, like Him, are in the image of God. All men and women are in the similitude of the universal Father and Mother, and are literally the sons and daughters of Deity.
This description is widely accepted by modern Latter-day Saints as fundamental to the plan of salvation. However, there are differences of opinion as to the nature of the premortal existence in other Latter Day Saint denominations.
The LDS Church teaches that during the premortal existence, there was a learning process which eventually led to the next necessary step in the premortal spirits' opportunity to progress. This next step included the need to gain a physical body that could experience pain, sorrow and joy and "walk by faith." According to this belief, these purposes were explained and discussed in councils in heaven, followed by the War in Heaven where Satan rebelled against the plan of Heavenly Father.
In Islam, all souls are believed to have been created in adult form (before earthly life) at the same time God created the father of Mankind, Adam. The Quran recounts the story of when the descendants of Adam were brought forth before God to testify that God alone is the Lord of creation and therefore only he is worthy of worship  so that on the Day of Judgement, people could not make the excuse that they only worshipped others because they were following the ways of their ancestors. Humans do not remember as they are born with an undeveloped mind (leaving only an innate awareness that he exists and is one, known as the Fitra) and he decreed at which point each and every human would be born into the physical world.
In the Bhagavad Gita, considered by Hindus to be a most holy scripture, Krishna tells Arjuna; "Never was there a time when I did not exist, nor you, nor all these kings; nor in the future shall any of us cease to be."
The Baha'i Writings refer in a number of places to at least three four key dimensions of pre-existence. Firstly, that the individual soul of a human being comes into being at the time of conception and only thereafter is eternal; in other words it is not pre-existent. Secondly, in distinction to the above, that the souls of the world’s greatest spiritual teachers, the founders of world religions, are pre-existent. Thirdly, that God, a reality which human consciousness can not comprehend, is pre-existent, that is he exists prior to time and to his creation. Fourthly, that the relationship between God and the phenomenal or contingent world is one of emanation, as the rays of the sun are to the sun. In other words, the pre-existent world of God remains separate from and does not descend into his creation.