The age of enlightenment was a time of new emphasis on, among a great many other things, obtaining knowledge through reason and structured logic. Even seeing "science" as a discreet concept (i.e. the scientific process) came to be in this time period.

Modernism was a shakeup and rejection of "realism"; post-modernism took it a step further by rejecting the notion of a universal truth entirely; the replacement idea is that what is true can only be discerned based on an individual's experience as we can only gain knowledge through imperfect means.