I am now to offer some thoughts upon that sameness or familiarity which we frequently find between passages in different authors without quotation. This may be one of three things either what is called Plagiarism, or Imitation, or Coincidence. – James Boswell, “The Hypochondriack,” No.XXII, 1779

Many moons ago dictionaries of quotations may have been less needed than they are today. In those good/bad old days, people walked around with entire poems and all the Shakespearean soliloquies in their heads…. – Joseph Epstein, Foreword to Fred R. Shapiro’s Yale Book of Quotations, 200

Reframing an extract as a quotation constitutes a kind of coauthorship. With no change in wording, the cited passage becomes different. I imagine that the thrill of making an anthology includes the opportunity to become such a coauthor. – Gary Saul Morson, The Words of Others: From Quotations to Culture, 2011