Reason as a theory and an epistomological method has been employed and debated for many centuries, but perhaps most influentially during the period of The Enlightenment .  It was during this period that a dominant ideology based on empiricism and reason flourished.  Enlightenment thinkers believed that through the use of reason, observation, and experience, all that there was to know about the world could become knowable.  Through calculation and training, a single body of knowledge about everything could be created, and society could progress toward perfection. 

Several theorists, however, disagreed with the idea that reason could be employed in such caluclating and consistent ways.  Kant, for example, was highly critical of this approach because it took for granted that humans process information in the exact same way – something he said was incorrect.  Kant argued that no amount of education or use of Reason would ever ensure that when we perceive and experience something, we perceive and experience it in an identical way as someone else, making the whole notion of an “objective body of knowledge” (which the Enlightenment thinkers believed to be knowable) totally incomprehensible.   He used the concepts of “noumena” and “phenomena” to theorize about the distinction between reality and perceptions of it.  Noumena are the things themselves, phenomena are our unique perceptions of the things, based on how our mind processes information.  Kant argues then, that truly “knowing” anything is impossible, and that we must acknowledge this fact rather than create entire fields of study based on the faulty notion that the world is innately accessible and objectively knowable.