The Enlightenment is the period in the history of western thought and culture, stretching roughly from the mid-decades of the seventeenth century through the eighteenth century, characterized by dramatic revolutions in science, philosophy, society and politics; these revolutions swept away the medieval world-view and ushered in our modern western world.
Enlightenment thought culminates historically in the political upheaval of the French Revolution, in which the traditional hierarchical political and social orders (the French monarchy, the privileges of the French nobility, the political power and authority of the Catholic Church) were violently destroyed and replaced by a political and social order informed by the Enlightenment ideals of freedom and equality for all, founded, ostensibly, upon principles of human reason.
The dramatic success of the new science in explaining the natural world, in accounting for a wide variety of phenomena by appeal to a relatively small number of elegant mathematical formulae, promotes philosophy (in the broad sense of the time, which includes natural science) from a handmaiden of theology, constrained by its purposes and methods, to an independent force with the power and authority to challenge the old and construct the new, in the realms both of theory and practice, on the basis of its own principles.
Many of the leading issues and positions of contemporary philosophical ethics take shape within the Enlightenment. Prior to the Enlightenment in the West, ethical reflection begins from and orients itself around religious doctrines concerning God and the afterlife. The highest good of humanity, and, accordingly, the content and grounding of moral duties, are conceived in immediately religious terms. During the Enlightenment, this changes, certainly within philosophy, but to some significant degree, within the population of western society at large. As the processes of industrialization, urbanization, and dissemination of education advance in this period, happiness in this life, rather than union with God in the next, becomes the highest end for more and more people.
Also, the violent religious wars that bloody Europe in the early modern period motivate the development of secular, this-worldly ethics, insofar as they indicate the failure of religious doctrines concerning God and the afterlife to establish a stable foundation for ethics. In the Enlightenment, philosophical thinkers confront the problem of developing ethical systems on a secular, broadly naturalistic basis for the first time since the rise of Christianity eclipsed the great classical ethical systems.
The general philosophical problem emerges in the Enlightenment of how to understand the source and grounding of ethical duties, and how to conceive the highest good for human beings, within a secular, broadly naturalistic context, and within the context of a transformed understanding of the natural world.
Deism. Deism is the form of religion most associated with the Enlightenment. According to deism, we can know by the natural light of reason that the universe is created and governed by a supreme intelligence; however, although this supreme being has a plan for creation from the beginning, the being does not interfere with creation; the deist typically rejects miracles and reliance on special revelation as a source of religious doctrine and belief, in favor of the natural light of reason. Thus, a deist typically rejects the divinity of Christ, as repugnant to reason; the deist typically demotes the figure of Jesus from agent of miraculous redemption to extraordinary moral teacher. Opposition to deism derives sometimes from the perception of it as coldly rationalistic. The God of the deists, arrived at through a priori or empirical argument and referred to as the Prime Mover or Original Architect, is often perceived as distant and unconcerned with the daily struggles of human existence, and thus as not answering the human needs from which religion springs in the first place.
Atheism. Atheism is more present in the French Enlightenment than elsewhere. In the writings of Denis Diderot, atheism is partly supported by an expansive, dynamic conception of nature. According to the viewpoint developed by Diderot, we ought to search for the principles of natural order within natural processes themselves, not in a supernatural being. Even if we don't yet know the internal principles for the ordering and development of natural forms, the appeal to a transcendent author of such things is reminiscent, to Diderot's ear, of the appeal to Aristotelian “substantial forms” that was expressly rejected at the beginning of modern science as explaining nothing.
I find that those who claim to be enlightened today do not have a flipping clue as to what they are talking about. This was about scientific and true moralistic and ethical thought, especially after the crusades and their bloody aftermath, not about divine intervention. Give me back my history and my constitution, not your twisted conservative and historically inaccurate view of it. Just Say'in :o)