The Enlightenment was an 18th century philosophical movement in Western Europe. 

It is a movement dedicated to the pursuit of truth as empirically discoverable. Enlightenment thinkers believe that by combining the power of Reason and observation, individuals can arrive at the Truth and progress towards perfection.

Enlightenment thinkers believe that there exists objectively understandable laws that govern nature, and by understanding these laws through the scientific method, a uniform and objective body of knowledge could be produced.   The philosophes admire Newton, an observer who used the scientific method to infer results. It is the unity of reason and observation that makes progress and the attainment of truth possible.  Newton believed that facts are discovered through observation rather than abstract reasoning and noticed that these facts show patterns and relationships. The Enlightenment is therefore a shift from a religious to a scientific mindset. Man can form ideas and understand the world around him through perception, the senses and experience, for knowledge exists in its immediacy. 

Enlightenment philosophers and scientists applied the scientific method not only to "science", but also to social systems, insitutions, relationships, and virtually all of humanity.  They saw the possibility that absolutely everything could be quantitatively measured and calcluated.  Seeing social systems as mechanistic and as having underlying Truths, philosophers attempted to rationally identify and replace the parts of society that were not progressive or functioning with the belief that by fixing these parts a more perfect society could be created.  Contrary to previous thought, they see humans as capable of critically examining the self and other aspects of humanity and coming to the same conclusion about reality.  They believe that intellectual progress was the basis of the journey towards the general  progress of humankind. By scientifically studying the nature of man and the environment in which he lives, humans can direct their focus to progress towards perfection.

More than just an epistomology, the Enlightenment also saw the rejection of religious dogma and superstition, criticisms of the state, and the advocacy of basic human freedoms.  The French Philosophes were particularly passionate about liberation from the oppression of the Catholic Church and from the State.  Most of all, the Enlightenment became an avenue for philosophical thought to translate into real world change, and was unique and powerful in its practical applications.

That is not to say that this dominant approach to reality went without criticisms.  Many social theorists, such as Kant and Michel Foucault, critique the empirical epistemology of the Enlightenment.

In Kant's essay What is Enlightenment? Kant argues that the mind is never able to fully perceive objective reality. In Kant’s perspective, the mind always filters its perception of reality and therefore interprets it subjectively. Kant uses the terms noumena and phenomena to describe this process. Noumena are the material things in the world that exist external from the individual while phenomena are things as we perceive them. Kant argues that we can only perceive the noumena in a phenomenal form. 

Kant is also critical of the empiricism of the Enlightenment is because he thinks it is important to recognize the limits of empiricism. According to Kant, there is knowledge that exists outside of empirical knowledge that is measured through other means than experiencing the external world. To illustrate this point, Kant discusses a priori categories, which exist in the mind and are separate from the “noumenal” world. Time and space both fall into these categories. The importance of a priori categories is that they are ideas rather than facts. Ideas, such as the mind’s construction of time, exist outside of the realm of empiricism and therefore cannot be measured using the epistemology of the Enlightenment.

Another aspect of the enlightenment Kant argued against was it's epistemology.  He believed that each individual should ‘reason for reason’s sake,’ rather than accepting prescribed ideas from society.  He believed that if our society is heavily structured by institutions, we have less room to question them and therefore cannot progress.  Also, such institutions would be based off of perceived ‘laws,’ which Kant would argue are faulty due to our erroneous, filtered perceptions.  Kant believed true progress lay in the individual’s ability to reason freely, which he felt would be inhibited by flawed societal institutions.

Michel Foucault

's essay, What is Enlightenment, discusses the "blackmail of the enlightenment".  Foucault argues that one does not have to be "for" or "against" the enlightenment.  He stresses that the Enlightenment was an event to be viewed in a historical and social context, not a system of thought that one must be a part of or not a part of.