All this is discouraging for a champion of footnotes like myself. The footnotes are among the first things I look at when I pull a book from a store shelf. My editor gamely tolerated my inclusion of many in my own book (though we removed more than we left in). I would be proud to be a footnote in someone else’s work.
Of course, scholarly books are still full of footnotes. The prototypic footnote is the source note, providing a citation for each proclamation in the text (early annotations were sometimes called “proofs”). These footnotes range from useful to pedantic, sometimes lending an air of authority, sometimes providing a map of the writer’s path. Legal writing in particular is rife with these footnotes, perhaps an acknowledgment that law is built on laws-past.
But I champion another species of footnote: the wandering footnote. These digressive notes, seeing a sentence that some might consider complete, determine to hijack it with a new set of ever more tangential facts. In the wayward note, the bumps and curves of the author’s mind seem to be laid plain on the paper. I came of intellectual age hearing the author’s sotto voce asides in the philosophy essays I loved. I still recall footnotes that begin, enticingly, “Imagine that . . . ”; “Consider . . . ”; or even, in one of J. L. Austin’s famous thought experiments, “You have a donkey. . . . ” I had the feeling of being taken into confidence by a wise fellow during an erudite lecture, and being told something even more clever and lucid.  
Full essay at The New York Times.

Alexandra Horowitz is the author of “Inside of a Dog: What Dogs See, Smell and Know.”