The great scholarly or anecdotal footnotes of Lecky, Gibbon, or Boswell, written by the author of the book himself to supplement, or even correct over several later editions, what he says in the primary text, are reassurances that the pursuit of truth doesn't have clear outer boundaries: it doesn't end with the book; restatement and self-disagreement and the enveloping sea of referenced authorities all continue. Footnotes are the finer-suckered surfaces that allow tentacular paragraphs to hold fast to the wider reality of the library.