Citing Correct Sources
An astonishing number of often-cited sayings attributed to famous people are incorrectly credited or dubiously attributed, even in the most respected quotation sources. The best research on this subject can be found in Ralph Keyes's
“America is great because America is good. If America ceases to be good, America will cease to be great.” Attributed to Alexis de Tocqueville, but no one really knows who said this.
“There is a principle which is a bar against all information … contempt prior to investigation.” Credited to the philosopher Herbert Spencer, it was actually written by theologian William Paley in 1794.
“You can fool all of the people some of the time; you can fool some of the people all of the time; but you can't fool all of the people all of the time.” Always attributed to President Lincoln, there is no evidence that he ever said this and the actual author is unknown.
“I disapprove of what you say, but will defend to the death your right to say it.” This is usually said to be a comment by Voltaire, but this was actually the way Voltaire biographer Evelyn Beatrice Hall portrayed the philosopher's attitude towards the writing of a colleague.
“If the only tool you have is a hammer, everything looks like a nail.” This has been ascribed to everyone from the Buddha to Mark Twain. The original idea was philosopher Abraham Kaplan's, stated in 1964, but this particular wording was formulated two years later by psychologist Abraham Maslow.
Of course, the point of the quotation is not who said it, but the thought, so if you are not sure of the source, just say, “someone once said” or note that it has been put into the mouths of many famous people. Even if you get the source wrong, no one in the audience is likely to care, but you should make some effort to get it right, in case someone does challenge the cited source.