I have since found that attitudes on footnotes tend toward the hyperbolic. One scholarly writing handbook celebrates the “cartwheel” of the footnote, while Grafton compares the drone of the historian’s footnote to “the high whine of the dentist’s drill,” a sign that we are in the presence of professionals. Legal footnotes — the subject of particularly contentious debate — are “a mother lode, a vein of purest gold,” one judge gushed, while another legal writer called them “lead feet below the line.” Footnotes are “a rhapsodic grace note” in a master’s hands, a journalist wrote. More often, however, footnotes are slandered as “forbidding,” “unsightly,” “like a fungus”; and even, as one footnote-weary professor put it, a “subversive breed of mice.” I have come across more than one author who chose “excrescence” to describe footnotes. Noël Coward reputedly said that “having to read a footnote resembles having to go downstairs to answer the door while in the midst of making love.”

The footnote jousting could soon be moot, as the e-book may inadvertently be driving footnotes to extinction. The e-book hasn’t killed the book; instead, it’s killing the “page.” Today’s e-readers scroll text continuously, eliminating the single preformed page, along with any text defined by being on its bottom. A spokesman for the Kindle assured me that it is at the discretion of the publisher how to treat footnotes. Most are demoted to hyperlinked endnotes or, worst of all, unlinked endnotes that require scrolling through the e-reader to access. Few of these will be read, to be sure.

I admit to being somewhat mystified that technological innovation is imperiling footnotes. Computers would seem to solve what I see as the main problem they pose — to wit, edging in the superscript numbers on a typewritten page and measuring just the right amount of space to leave at the bottom. Footnotes really presage hyperlinks, the ultimate interrupter of a stream of thought. (But footnotes are far superior: while hyperlinks can be highly useful, one never finds oneself looking at an error message at the bottom of the page where a footnote used to be.) Even the audio book has solved the problem of how to convey footnotes. Listen to David Foster Wallace reading his essay collection “Consider the Lobster,” with its ubiquitous show-stealing asides: at a certain point, his voice is unnaturally distant, the result of a production trick intended to represent the small type of a footnote. Wallace’s e-book was not immune to de-footnoting, though; all these crucial asides now appear at the end of the book in the Kindle and iPad versions. Even the Kindle edition of Zerby’s history of the footnote is now full of endnotes instead.

Should footnotes fully disappear, I would grieve their loss. I do not find it disagreeable to bend my nose south and find further information where it lands. Surely the purpose of a book is not to present a methodically linear narrative, never wavering from its course, with no superfluous commentary set off by commas. In my mind, footnotes are simply another punctuative style: a subspecies of parenthesis that tells the reader: “I’ve got something else here you might like! (Read it later.)” What better thing? You get to follow the slipstreams in the author’s thinking at your own leisure.

A footnote: I’ve kept this essay annotation-free. But every sentence could have had a footnote, providing a source, further reading, a tangent, an explanation. Is the essay really better without them?