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I have also found what appear to be three spurious attributions of the "stages of truth" quote. The most prevalent is the following version:
All truth passes through three stages. First, it is ridiculed. Second, it is violently opposed. Third, it is accepted as self-evident.
This quotation and its minor variants, which may be found on many Internet web sites, Usenet news postings, and letters to the editor of newspapers, is nearly always attributed to Arthur Schopenhauer. For example, see [26, p. 93].
However, I have not found this particular quotation in Schopenhauer's writings; neither have Schopenhauer experts that I have consulted been able to produce a citation.
Why has this quotation come to be attributed to Schopenhauer? It seems likely this is due in part to its citation in a popular book of quotations, first published in 1981, that has since gone through several different titles and printings .
In the United States, it is called The Harper Book of Quotations, and the quotation appears, for example, on page 451 of the 3rd edition:
Every truth passes through three stages before it is recognized. In the first it is ridiculed, in the second it is opposed, in the third it is regarded as self-evident.