This article presents enlightenment in the sense of any transformation into greater wisdom. For other views or essays on enlightenment, see Meditation, Mysticism (including authors such as Carlos Castaneda), Moksha (a Hindu term), and enlightenment (Buddhism).
__Kant's definition of enlightenment__
In his famous 1784 essay "What Is Enlightenment?", Immanuel Kant defined it as follows:
"Enlightenment is man's leaving his self-caused immaturity. Immaturity is the incapacity to use one's own understanding without the guidance of another. Such immaturity is self-caused if its cause is not lack of intelligence, but by lack of determination and courage to use one's intelligence without being guided by another. The motto of enlightenment is therefore: Sapere aude! Have courage to use your own intelligence!"
__Spirituality and enlightenment__
Enlightenment as a concept, is related to the Buddhist Bodhi. It is a cornerstone of religious and spiritual understanding in many, but not all religions. (Its counterparts, the Christian and Judaic ideas of spiritual knowledge used the concept called divine illumination.) Systematic search for enlightenment was a goal of the seekers after they found their master teachers or gurus, who could guide them. However, this formulation was not necessarily spiritual. In earlier times, such as during the Bon period of Tibetan religion, it was essentially magical, which is a pre-scientific stage. After the systematic methods were learned in India, the nations of Asia made pilgrimages to learn them. The relationship between seeker and guru was and remains, in most cases, an essential point for Enlightenment. There are practical signs of such a state, which can be recognized by a guru. Thus there is a practical, even secular component to Enlightenment, which differs from the requirement of Christian divine grace from God, which was essentially mystical or sacred.
Note that the Christian saints, who stood outside the religious hierarchy, attained their spiritual standing on their own and could not communicate the practical means toward illumination, like Saint Francis of Assisi. Instead, the Christian saints were frequently adjoined into spiritual orders, like Mother Teresa in the twentieth century. Thus, in the case of St. Francis, huge wealth was channelled into their orders, in complete disregard of his motivation. Baldly put, the Christian ideas were used to make money, the primary motivation for the Age of Exploration.
During the period after the Age of Exploration when Portuguese, and later, English trading companies were gaining hegemony over the rajahs of India, the concept of Enlightenment started filtering into Europe. Concurrently, when Isaac Newton's System of the World was being formulated and then exploited, it was realized that a mystical view of the world could be discarded. This program was called the Enlightenment. Thus the Christian viewpoint was systematically suppressed, culminating in the secular viewpoint expressed in the American Revolution, and tragically in the violent actions of the French Revolution against the King, the First Estate (the Church) and the Second Estate (the nobility).
This intellectual history of term "enlightenment" is the basis for the secular idea that relates to a localized, religion-specific "enlightenment", and also attempts to bridge the traditional gap between religions and religious belief and psychological science.
The "age of enlightenment" is a proverbial time of maturing in people -- roughly around the age of 18 years -- when the illusions of childhood lift, and one is left with greater self-awareness and understanding of their own roles and responsibilities in the world. This is analogous to the Christian-adopted concept of being "born-again" and is a direct tie between the spiritual teachings of The Christ, Jesus and Buddha. In Buddhism, enlightenment means one is ultimately free from the cycle of suffering and rebirth thus never have to be born again except by choice, to save others, by aiding others in the path toward Enlightenment.
In our own time, Jiddu Krishnamurti attained Enlightenment under a pepper tree in Ojai, California in the 1920s. He has influenced, among others, the physicist David Bohm (considered an outcaste from physics, but not wholly scorned by some), and a surprising number of seekers in California and also world-wide, to this day.