In 2005 Harry Frankfurt re-published a wonderful philosophical essay, 'On Bullshit', which became a bestseller. Also in 2005 Stephen Colbert introduced a new word, 'Truthiness' - "the quality of preferring concepts or facts one wishes to be true, rather than concepts or facts known to be true" - which became Merriam Webster's word of the year.
Both these terms are motivated by concern about the decline of public discourse in America, and their popularity suggests that many people share that concern. Yet they differ in their specific diagnoses of the problem. Bullshit is a form of artful deception of audiences by speakers; truthiness is a collaborative exercise in self-deception in which the audience is a willing participant. Bullshit denotes an abuse of a position of authority, such as by TV pseudo-scientists or politicians; truthiness is a radically democratic view of truth as a matter of personal opinion - whatever one finds it agreeable to believe. Bullshit is what the left thinks rightist politicians do to win votes; truthiness is how they actually succeed.