"The compound word post-truth exemplifies an expansion in the meaning of the prefix post- that has become increasingly prominent in recent years. Rather than simply referring to the time after a specified situation or event – as in post-war or post-match – the prefix in post-truth has a meaning more like ‘belonging to a time in which the specified concept has become unimportant or irrelevant’. This nuance seems to have originated in the mid-20th century, in formations such as post-national (1945) and post-racial (1971).
Post-truth seems to have been first used in this meaning in a 1992 essay by the late Serbian-American playwright Steve Tesich in The Nation magazine. Reflecting on the Iran-Contra scandal and the Persian Gulf War, Tesich lamented that ‘we, as a free people, have freely decided that we want to live in some post-truth world’. There is evidence of the phrase ‘post-truth’ being used before Tesich’s article, but apparently with the transparent meaning ‘after the truth was known’, and not with the new implication that truth itself has become irrelevant.
A book, The Post-truth Era, by Ralph Keyes appeared in 2004, and in 2005 American comedian Stephen Colbert popularized an informal word relating to the same concept: truthiness, defined by Oxford Dictionaries as ‘the quality of seeming or being felt to be true, even if not necessarily true’. Post-truth extends that notion from an isolated quality of particular assertions to a general characteristic of our age."