Quotation:  "All tyranny needs to gain a foothold is for people of good conscience to remain silent."

Variations: This quotation has hundreds of variations, which generally are composed of some combination of the following components: 
(All that is necessary/needed/required) OR (all it takes) OR (the best way)) for evil to (triumph OR succeed OR prosper OR prevail OR "win in the world" OR "gain a foothold") is for ("good men" OR "good people" OR "good men and women" OR "people of good conscience") to ("do nothing" OR "say nothing" OR "remain silent")

Sources consulted:

1. Papers of Thomas Jefferson Digital Edition
2. Thomas Jefferson Retirement Papers
3. Thomas Jefferson: Papers collection in Hathi Trust Digital Library

Earliest known appearance in print, attributed to Jefferson: 2005^[1]

Status: This quotation has not been found anywhere in Thomas Jefferson's writings.  Curiously, the variant of this quotation almost exclusively attributed to Jefferson is "all tyranny needs to gain a foothold is for people of good conscience to remain silent."  Other variants are not attributed to Jefferson at all, but typically to Edmund Burke and others.  This quotation has never been positively attributed to any specific person, at least in the forms above.  Edmund Burke is the figure most often credited with this quotation, although it has never been found in his writings.  The Yale Book of Quotations notes the earliest attribution of this quotation to Burke at 1950 (an unsourced attribution in the Washington Post), but the most convincing possible source of the quotation suggested to date is John Stuart Mill, in an address at the University of St. Andrews in 1867: "Bad men need nothing more to compass their ends than that good men should look on and do nothing."^[2] 

- Anna Berkes, 9/13/12

Further Sources

• Porter, Martin.  "‘All that is necessary for the triumph of evil is that good men do nothing’ (or words to that effect): a Study of a Web Quotation."  2002.  
• Quote Investigator.  "The Only Thing Necessary for the Triumph of Evil is that Good Men Do Nothing."  December 4, 2010.